Objective: Green tea extract (GTEs), including catechins and caffeine, have strong anti-microbial activity. Methods: We determined the anti-microbial and anti-fungal effects of a GTE on the vaginal pathogens, Proteus mirabilis (KCTC 2510), Streptococcus pyogenes (KCTC 3096), and Candida albicans (KCTC 7270). Results: The growth inhibitory effects of a GTE and the ethyl acetate fraction against P. mirabilis and S. pyogenes were stronger compared to the anti-microbial activity of the H2O fraction. Among the catechins, epigallocatechin gallate had the strongest anti-microbial activity. The growth of C. albicans was strongly inhibited by the methylene chloride fraction and caffeine; the anti-fungal activity of a GTE was due to caffeine. We also evaluated whether the in vitro activity of a GTE included purified solvent fractions stable to heat and pH changes. The stability of transtype catechins increased following heat treatment, but this did not significantly affect the anti-microbial activity. A GTE were stable over the pH range 4-10. The most active anti-microbial activity of a GTE occurred in an alkaline, rather than an acid environment, except for the anti-microbial activity against S. pyogenes and C. albicans, which was not influenced by pH. Conclusions: Taken together, the results of this study indicate that a GTE may be a valuable therapeutic agent for the treatment of vaginal pathogens.