Chemically, soy contains a group of phytoestrogens called isoflavones, predominantly genistein and daidzein. The aim of the present study was to determine the effects of post weaning consumption of dietary soy isoflavones on prepubertal and postpubertal serum levels of some reproductive hormones of male Wistar rats. The study involved investigating the effects of different doses of isoflavones in the diet. Male rats were weaned on either soy isoflavone free diet or on isoflavone containing diets, formulated by adding increasing amounts of Novasoy, a commercially available isoflavone supplement to the isoflavone free diet to give varying concentrations of isoflavones. Three isoflavone containing diets were used and these had 74.5, 235.6 and 1046.6 mg total isoflavones/kg pelleted diet. These diets represented the isoflavone concentration lower, equal to and more than that found in soy-based infant formulas respectively. The results obtained showed that; administration of low doses soy isoflavones (74.5 mg/kg) produced significant (p < 0.05) increase in serum Antimullerian Hormone levels both in prepubertal and post pubertal rats, when compared to the control groups. Administration of moderate doses of isoflavones (235.6 mg/kg) produced significant (p < 0.05) increase in serum levels of Antimullerian Hormone and Inhibin in both prepubertal and post pubertal rats when compared to the control groups. Administration of high doses of isoflavones (1046.6 mg/kg) produced significant (p < 0.05) increase in serum levels of Inhibin in both prepubertal and post pubertal rats when compared to the control groups. From this study, it was concluded that post-weaning consumption soy isoflavones produced significant changes in How to cite this paper: Godfrey, S., Daniel, E.E., Oluwadare, S.S. and Yovani, B. 12serum Inhibin and Antimullerian Hormone both in prepubertal and post pubertal male Wistar rats and the changes were dose dependent.