Abstract: Betamethasone stimulates production of necessary enzymes for reducing inflammatory responses. This drug is a long-acting steroid which produces quick anti inflammatory effects with long time effect. Effects of betamethasone on sexual hormes of female mice were studied in this study. Mice were divided in five groups (control, placebo and three treatments groups) with ten members in each group. Samples were kept in similar condition be synchronized in estrus cycle. Betamethasone was prepared in 0.1, 0.5 and 1 mg kg-1 doses and injected in peritoneum for 20 days. Control group was not injected while placebo received normal saline. After ten injections blood samples were prepared and the amounts of LH, FSH, strogen and progestron hormones were evaluated by RIA Method. Obtained results showed that strogen, progesterone and LH were reduced by all treatment significantly whereas FSH was increased in 0.5 and 1 mg kg-1 groups. According to results, betamethasone affects sexual hormones dose dependently and then can affect female sexual potential.