Abstract: OBJECTIVE To establish a bioassay method for Lepidogrammitis drymoglossoides(Bak.) Ching. METHODS Three methods including water extraction, ethanol extraction, and water extraction plus ethanol subsiding method were used to extract the bioactive components from Lepidogrammitis drymoglossoides(Bak.) Ching, and the anti-bacterial effect of each extraction was detected by the anti-bacterial test in vitro. The standard bacterium strain and the dose range of the medicine were selected. We ploted the curve of dose-effect of Lepidogrammitis drymoglossoides(Bak.) Ching in response to sensitive bacterium strains and established an effective model applied to one-point method. RESULTS The water extraction of Lepidogrammitis drymoglossoides(Bak.) Ching showed the diameter of its inhibition zone to CMCC 26003 strain was 17.39 mm. There was a good linear correlation between logarithm dosages and effect of Lepidogrammitis drymoglossoides(Bak.) Ching when its concentrations ranged from 0.25 to 1.25 g·mL^-1. CONCLUSION The bioassay method is one of the quality control methods of Lepidogrammitis drymoglossoides(Bak.) Ching, which is simple, reasonable and feasible.