The present study applied Ajzen’s theory of planned behavior (TPB) to explain intention to seek mental health services. It aimed to compare the traditional TPB model and the TPB partial mediation model in explaining help-seeking intention. It also aimed to understand the reasons for underutilization of mental health services in Macao in order to inform local policies. Finally, the effects of symptom severity, prior help-seeking, and gender were also examined. The present study consisted of two phases: a) a pilot study to develop belief-based measures used in the main study, and b) a cross-sectional study to investigate the application of TPB in understanding help-seeking intention. In the main study, 337 Macao residents (age range 18-65) participated in the survey conducted in the community. Results showed that the TPB partial mediation model is better than the TPB traditional model in explaining helpseeking intention. The model suggested that attitude, subjective norm, and perceived behavioral control were all significant predictors of help-seeking intention. However, symptom severity, prior help-seeking, and gender did not significantly predict help-seeking intention. The implications of these finding were discussed in relation to the salient beliefs about help-seeking elicited in the pilot study. Limitations and recommendations for future research are provided.