ABSTRACT:We aimed to determine the vitellogenin gene expression in response to 17β-estradiol (E2) treatment in livers of immature female Chinese edible frogs (Hoplobatrachus rugulosus). Frogs reared during rainy or dry seasons were intramuscularly injected daily with E2 at doses of 0, 50, 500, or 5000 µg/kg body weight for five days. During the rainy season, treatment with E2 within the dose range studied significantly decreased the vitellogenin gene transcript levels compared to those of the control. In contrast, during the dry season, treatment with E2 at all doses tended to increase the vitellogenin gene transcript levels. The endogenous plasma E2 levels in frogs reared during the rainy season were higher than those reared during the dry season. There was no significant difference in liver-somatic index or gonadosomatic index among the treated frogs during the rainy season. However, during the dry season, the 500 µg/kg E2 treatment significantly increased the frog liver-somatic index. The hepatocytes from the dry season frogs appeared smaller and flatter. The histology of ovaries from rainy season frogs showed that the oocytes were bigger and of several stages. We therefore concluded that the injection of E2 into immature female H. rugulosus may stimulate vitellogenesis if administered during the dry season, when the endogenous E2 is lower. This knowledge could be used as a basis for inducing precocious maturation or mating of H. rugulosus outside the breeding season.