Isoflavones and lignans, two major groups of phytoestrogens, have been postulated to have multiple health benefits, including anti-estrogenic, anti-cancer, pro-cardiovascular health, and ameliorating menopausal symptoms. Urinary excretion of isoflavonoids, including daidzein, genistein, glycitein, O-desmethylangolensin (O-DMA), dihydro-daidzein, dihydrogenistein, and equol, and lignans, including enterodiol and enterolactone, have been used as biomarkers of phytoestrogen exposure in epidemiologic studies. We evaluated the urinary excretion of phytoestrogens and their correlations with lifestyle and dietary factors among 2,165 women who participated in the Shanghai Women's Health Study (SWHS), a population-based prospective cohort study of 74,942 urban Chinese women aged 40-70 years at study enrollment (1996-2000). The medians (in nmol/mg creatinine) were: isoflavonoids, 17.13; daidzein, 5.57; genistein, 2.41; glycitein, 0.94; O-DMA, 1.52; dihydrodaidzein, 0.81; dihydrogenistein, 0.19; equol, 0.11; enterodiol, 0.30; and enterolactone, 1.18. These levels are 2- (enterodiol) to 126- (O-DMA) fold higher than levels among US women similar in age range with the exception of enterolactone, for which a similar level was observed for both populations. Urinary isoflavonoid excretion was higher among older women and women who engaged in regular exercise and significantly associated with soy food intake, but was inversely related to fruit intake. Urinary excretions of dihydrodaidzein, dihydrogenistein, equol, enterodiol, and enterolactone were inversely associated with body mass index (BMI). Urinary excretion of isoflavones correlated with soy food intake and healthy lifestyle but was inversely associated with fruit intake among middle-aged and elderly Chinese women. Our study adds important information to the rapidly growing body of research on the potential health benefits of phytoestrogens.