Cordyceps sinensis is a well-known and precious herb in traditional Chinese medicines. Since natural C. sinensis is very rare and is not sufficient to meet its increasing demand, mycelia fermentation has become a major and more economical source of C. sinensis materials. In our previous studies, a novel C. sinensis fungal strain UM01 was isolated from natural C. sinensis. The main bioactive compound is polysaccharide and it has markedly exhibited immuno-modulatory activities. In this thesis, the method for extraction, purification and characterization of polysaccharides from a novel C. sinensis fungus UM01 were investigated. A simple HPTLC method for the determination of polysaccharides from Cordyceps species was developed. The major achievements of this thesis are summarized as follows: (1) Microwave-assisted extraction (MAE) method was firstly developed for extraction of polysaccharides from cultured C. sinensis. The optimized condition for MAE was determined as a 60-fold water volume to mycelia, 1300 W microwave power and 5 min microwave irradiation time, generating the highest extraction yields of 6.20% total polysaccharides. (2) Purification of polysaccharides from a novel C. sinensis fungus UM01 was accomplished successfully. Three purified polysaccharides, UM01-S1, UM01-S4 and UM01-S6, were obtained. Chemical structure of polysaccharides were identified by infrared spectroscopy, SDS-PAGE, PACE, HPLC, GC-MS, and NMR analysis. The chemical properties of polysaccharides from C. sinensis UM01 could help to better understand structure-bioactivity relationships. (3) Physical properties and chain conformation of polysaccharides were examined using a refractometer, dynamic light scattering, static light scattering, and a vicosmeter. Chain conformation of polysaccharides was predicted using a polymer theory. iii (4) A cost-effective HPTLC method was developed and it was able to analyze the polysaccharides from natural C. sinensis, cultured C. sinensis and other Cordyceps species. These methods result in a simple, rapid and simultaneous analysis of parallel samples using a low-cost plate. In conclusion, chain conformation and structurally well-defined polysaccharides from cultured C. sinensis fungus UM01 are of great importance for revealing their structure-bioactivity relationship; they are of great interest for the development of a substitute for natural C. sinensis for new pharmacophores and new therapies. Furthermore, a simple HPTLC method is a useful approach for quality control of polysaccharides from Cordyceps species. The HPTLC method could be used as an analytical tool in routine analyses, it is beneficial for national usage of commercial Cordyceps products.