To obtain an antichlamidial agent which shows antimicrobial effect, e.g. detergency, disinfection or the like, on chlamidia, exhibits increased antimicrobial effect on chlamidia particularly before or just after infection and exerts excellent infection prophylactic effect or detergent effect.

This antichlamidial agent is obtained by including an extract obtained by using a bamboo, e.g. Phyllostachys pubescens or the like, and an alcohol or ether as an extraction raw material and an extracting solvent, respectively, as an active ingredient. This antichlamidial agent contains benzoquinone in the extract, increases the infection preventive effect of somatic cells on infectious elementary bodies(EB) in the life cycle of chlamidia and exhibits a certain antimicrobial effect due to annihilating intracellular reticular bodies(RB). Further, the more certain antimicrobial effect is exhibited when the extract contains liquid benzoquinone in a formation amount of 0.2-5 vol.%.