The present invention provides agents for preventing and/or improving endometriosis, which contain lactic acid bacteria of the genus Lactobacillus, in particular, Lactobacillus gasseri strain OLL2809. The present invention also provides food and beverage compositions for preventing and/or improving endometriosis, which contain the lactic acid bacteria, and methods for preventing and/or improving endometriosis which comprise administering the lactic acid bacteria.