Abstract: Objective To observe the effect of soy isoflavones on main serum sex hormones and ovaries in aged female rats.Methods Fifty 20-month-old female rats were randomly divided into five groups:control group(with oral gavage of normal saline),low-,moderate-,and high-dose group(with oral gavage of soy isoflavones of 100,200,and 300 mg·kg^-1),estrogen group(with oral gavage of diethylstilbestrol of 0.6 mg·kg^-1).After 8 weeks' of treatments,the levels of estradiol,progesterone,testosterone,luteinizing hormone(LH),follicle stimulating hormone(FSH),and sex hormone binding globulin(SHBG)in serum of the rats were detected with enzyme-linked immunosorbent assay(ELISA).Results Compared with those of the control group,the ratio of ovary/body(0.031±0.008),serum LH(3.225±0.405 ng/L) and FSH(1.536±0.186 IU/L) decreased(P<0.05 for all),whereas the serum estradiol(5.177±0.453 μg/L) increased(P<0.05) for the rats of high-dose soy isoflavones group,but no significant differences in uterus/body ratio,serum progesterone,testosterone,and SHBG were observed(P>0.05)in the rats of soy isoflavones groups.Conclusion Soy isoflavone could regulate serum levels of main sex hormones and alleviate the decline of ovarian function in aged female rats.