The objective was to evaluate the toxicity effect of gossypol on ultrastructure of mouse testis and the expression of Bax mRNA and Bcl-2 mRNA of sperm cells in mice.Forty-eight male mice were randomly divided into four groups:control group,L-group(30 mg·kg~(-1)·d),M-group(60 mg·kg~(-1)·d)and H-group(120 mg·kg~(-1)·d)and were orally administrated with gossypol diluted by sodium carboxymethyl cellulose(SCC)or SCC(control group)for 20 days.On the 21st day,all the mice were killed and ultrastructure changes of testis were observed by TEM.mRNA expression of Bax and Bcl-2 in testis was measured by semiquantitative RT-PCR.The results showed that the testicular ultrastructure in three treated groups was gradually damaged,according to the dosage of gossypol and cellular structure disordered and organelle degenerated,manifesting vacuolation of mitochondria,expansion of endoplasmic reticulum.mRNA expression of Bcl-2 in testis significantly increased(p<0.05)in L-group and then significantly decreased(p<0.05,p<0.01)in M-group and H-group compared with that in the control group;mRNA expression of Bcl-2 in M-group and H-group significantly decreased(p<0.05,p<0.01)than that in L-group and Bcl-2 mRNA expression in H-group showed a significant decrease(p<0.05)compared with that in M-group.On the other hand,mRNA expression of Bax significant increased(p<0.05,p<0.01)in M-group and H-group than that in the control group.The ratio of Bcl-2/Bax significantly reduced(p<0.05,p<0.01)in the treated group than that in the control group and was found to be an obvious dose-dependent.It demonstrated that the gossypol could induce the changes on ultrastructure of mice testis,down-regulate mRNA expression of Bcl-2 and up-regulate mRNA expression of Bax,which indicated that sperm cells were induced apoptosis. The objective was to evaluate the toxicity effect of gossypol on ultrastructure of mouse testis and the expression of Bax mRNA and Bcl-2 mRNA of sperm cells in mice. Forty-eight male mice were differentiated into four groups: control group, L-group (30 mg · kg -1 · d), M-group (60 mg · kg -1 · d) and H-group (120 mg · kg -1 · d) and were orally administrated with gossypol diluted by sodium carboxymethyl cellulose (SCC) or SCC (control group) for 20 days. On the 21st day, all the mice were killed and ultrastructure changes of testis were observed by TEM.mRNA expression of Bax and Bcl-2 in testis was measured by semiquantitative RT-PCR. The results showed that the testicular ultrastructure in three treated groups was gradually damaged, according to the dosage of gossypol and cellular structure disordered and organelle degenerated, manifesting vacuolation of mitochondria, expansion of endoplasmic reticulum .mRNA expression of Bcl-2 in testis significantly increased (p <0.05) in L-group and then significantly decreased (p <0.05, p <0.01) in M-group and H-group compared with that in the control group; mRNA expression of Bcl-2 in M-group and H- ) than that in L-group and Bcl-2 mRNA expression in H-group showed a significant decrease (p <0.05) compared with that in M-group. the ratio of Bcl-2 / Bax significantly reduced (p <0.05, p <0.01) in the treated group than that in the control group and was found to be an obvious dose-dependent.It demonstrated that the gossypol could induce the changes on ultrastructure of mice testis, down-regulate mRNA expression of Bcl-2 and up-regulate mRNA expression of Bax, which indicates that sperm cells were induced apoptosis .