It was about the initially research in the kinetics of inhibiting acetylcholinesterase(AChE)of endophytic fungi g5 which Isolated from Huperzia serrata. In addition, morphologic determination was done with this fungus. The effect of EtOH extraction from g5 fermentative product on the inhibiting AChE was detected by coloration of DTNB method, and this fungus was determinated by slide culture. The result is that g5 belongs to Penicillium rugulosum. According to Initially analysis of enzyme kinetics, it was showed that g5 was admixed competitive reversible inhibitory type, and the inhibit-constant KI against free E and KIS against comoles compound of ES is 0.0789 mL and 1.1352 mL, respectively. The metabolic product of g5 can be developed as potential drugs which is not only conspicuous but also reversible inhibiting AChE in vitro.