Abstract: AIM To compare the content of nucleosides from natural Cordyceps sinensis and cultured Cordyceps mycelia, and the effect of humidity and heat on the contents of nucleosides. METHODS The contents of nucleosides were determined using high performance capillary electrophoresis (HPCE). Beckman P/ACE System 5010 apparatus equipped with a UV detector and a Beckman untreated fused silica capillary (57 cm×75 μm, 50 cm effective length) were used. Before sample injection, the capillary was rinsed with 1 mol·L^-1 sodium hydroxide and running buffer for 5 minutes, respectively. 20 kV was applied during separation. Pressure injection was 586 kPa for 6 seconds, and the wavelength of detector was 254 nm. The running time was 20 minutes at 20℃. The effect of humidity and heat on the content of nucleosides from natural Cordyceps sinensis and cultured Cordyceps mycelia was observed for 1, 3, 5 and 10 days at temperature 40℃, and relative humidity 75%. RESULTS The contents of nucleosides from cultured Cordyceps mycelia were higher than that of those from natural Cordyceps sinensis. The contents of nucleosides from freshly collected natural Cordyceps sinensis, were under the detection limit. The contents of nucleosides from natural Cordyceps sinensis were significantly increased by effect of humidity and heat, the phenomenon was not observed in cultured Cordyceps mycelia. CONCLUSION There are difference in nucleosides content between natural Cordyceps sinensis and cultured Cordyceps mycelia. The nucleosides in natural Cordyceps sinensis may be derived from the degradation of macro molecular nucleic acids. That means it is probably controversial that adenosine was used for quality control of natural Cordyceps sinensis.