Rare earth elements (REES), in particular, cerium and lanthanum oxide nanoparticles, have undergone a steady spread in several industrial, agriculture and medical applications, which have attracted much concern for their effects on human health. However, most of the works addressing cerium and lanthanum oxide nanoparticles toxicity have only used in vitro models or in vivo intratracheal instillation methods. The toxicity studies have varied results and not all are conclusive. The information about risk assessments derived from epidemiology studies is severely lacking. The knowledge of occupational safety and health (OSH) for exposed workers is very little. Human biological monitoring (HBM) was defined as "the measurement and assessment of agents or their metabolites either in tissues, secreta, excreta, expired air or any combination of these to evaluate exposure and health risk compared to an appropriate reference." Based on the difference of indicators for internal dose and effect, respectively, HBM can be divided into monitoring of exposure and monitoring of effects. With the aim of exploring a sensitive and reliable indicator of estimating exposure level to REEs, a simple, accurate and specific ICP-MS method for simultaneous direct quantification of 15 REES (89Y, 139La, 140Ce, 141Pr, 146Nd, 147Sm, 153Eu, 157Gd, 159Tb, 163Dy, 165Ho, 166Er, 169Tm, 172Yb and 175Lu) in human urine has been developed and validated. The method showed good linearity for all REEs in human in the concentrations ranging from 0.001-1.000μg·L-1 with r²>0.997. The limits of detection and quantification for this method were in the range of 0.009-0.010μg·L-1 and 0.029-0.037μg·L-1, the recoveries on spiked samples of the 15 REEs ranged from 93.3% to 103.0% and the relative percentage differences were less than 6.2% in duplicate samples, and the intra- and inter-day variations of the analysis were less than 1.28% and less than 0.85% for all REES, respectively. The developed method was successfully applied to the determination of 15 REEs in 31 urine samples obtained from the control subjects and the workers engaged in work with manufacturing of ultrafine and nanoparticles containing cerium and lanthanum oxide. The results suggested that only the urinary levels of La (1.234 ± 0.626 μg·L-1), Ce (1.492 ± 0.995μg·L-1), Nd (0.014 ± 0.009μg·L-1) and Gd (0.023 ± 0.010μg·L-1) among the exposed workers were significantly higher (p＜0.05) than the levels measured in the control subjects. From these, La and Ce were the primary components, and accounted for 88% of the total REEs. Lanthanum comprised 27% of the total REEs while Ce made up the majority of REEs content at 61%. The remaining elements only made up 1% each, with the exception of Dy which was not detected. Comparison with the previously published data, the levels of urinary La and Ce in workers and the control subjects show a higher trend than previous reports. In order to assess occupational exposure level of 15 rare earth elements (REEs) and identify the associated influence, and further verify the accuracy and precision of simultaneous direct quantification of 15 REEs ICP-MS method, we used the conventional routine methods, inductively coupled plasma mass spectrometry (ICP-MS) based on closed-vessel microwave-assisted wet digestion procedure, to determinate the concentration of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu in urinary samples obtained from workers producing ultrafine and nanoparticles containing cerium and lanthanum oxide. The results suggest that La and Ce were the primary component, together accounting for 97 percent of total REEs in workers. The urinary levels of La, and Ce among the workers (6.36, 15.32μg·g-1 creatinine, respectively) were significantly enriched compared to those levels measured in the control subjects (1.52, 4.04μg·g-1 creatinine, respectively) (p＜0.05). This study simultaneously identified the associated individual factors, the results indicate that the concentrations in over 5 work years group (11.64±10.93 for La, 27.83±24.38 for Ce) were significantly elevated compared to 1-5 work years group (2.58±1.51 for La, 6.87±3.90 for Ce)(p＜0.05). Compared the urinary levels of La and Ce at the separation and packaging locations (9.10±9.51 for La, 22.29±21.01 for Ce) with the other locations (2.85±0.98 for La, 6.37+2.12 for Ce), the results show urinary concentrations were significantly higher in workers at separation and packaging locations (p < 0.01). Inter-individual variation in levels of La and Ce in urine is the result of multi-factorial comprehensive action. Further researches should focus on the multiple factors contributing to the REEs levels of the occupationally exposed workers. Simultaneously, to establish the relationship of associated exposure and hazard effects, a cross-sectional occupational epidemiological health survey and occupational medical surveillance programs and experimental studies were conducted in all consenting workers manufacturing of ultrafine and nanoparticles containing cerium and lanthanum oxide. The results show that some health hazards, such as hypertension, cardiovascular and cerebrovascular diseases (CCVD), fatty liver, hepatic dysfunction, renal dysfunction, dyslipidemia existed in exposed workers. The five leading disease was hepatic dysfunction (18.1%), dyslipidemia(15.5%), cardiovascular and cerebrovascular diseases (CCVD) (8.6%), fatty liver (7.8%), abnormal urine (6.0%). Hepatic dysfunction, renal dysfunction, CCVD, and dyslipidemia were highest for the workers in weighing, measuring, grinding and subdividing operations. Key words: rare earth elements (REEs); cerium and lanthanum oxide nanoparticles; inductively coupled plasma-mass spectrometry (ICP-MS); urine; human bio-monitoring; health assessment