Objective To study the effects of FSH on the phosphorylation of Smad2/Smad3 protein in rat ovarian granulosa cells. Methods The granulosa cells of 21-day-old SD female rats were cultured with TGFβRⅡ antibody and FSH of different concentrations,and then the cells were obtained at defined points to determine the phosphorylation of Smad2/Smad3 by immunocytochemistry. Results 1. Both Smad2 and Smad3 proteins were mainly expressed in the cytoplasm of ovarian granulosa cells,and a small amount of phosphorylatedSmad2/3 were expressed in the nucleus; 2.The treatment with FSH increased the nuclear transfer of Smad2/Smad3 and the expression of P-Smad2/P-Smad3 in granulosa cells,The effects of FSH were time and dose dependent; 3.The antibody-neutlised TGFβRⅡ inhibited the stimulation of FSH on Smad2/3 in granulosa cells. Conclusion 1.FSH stimulates the phosphorylation of Smad2/Smad3;