Objective: To investigate the effects of pregestational and gestational exposure to an isoflavone of sexually mature female mice on their reproductive health and on the postnatal development of their offspring. Methods: Sexually-mature ICR female mice were randomly segregated into Control group 1 that was given the normal diet consisting of food pellets, Control group 2 that was given food pellets with additional c oil of 2 mL/kg bodyweight. The three (3) isoflavone treatment groups were given 50 mg/kg body weight, 100 mg/kg body weight and 150 mg/kg body weight for low dose (LD), medium dose (MD) and high dose (HD) respectively. Treatments were administered 2 weeks prior to mating and gestation and thereafter until parturition. The delivered pups were weaned up until 21 days. On the 21st day, postnatal development were determined, excluding the birth weight of pups which was measured one day post-parturition. The dams were sacrificed as well and the markers of matal health were determined. Results: There were no significant differences found between the control groups and the treatment groups in terms of the markers of matal reproductive health. For postnatal development, only HD group displayed a significantly higher mean AGD from the other groups. Conclusions: The data implies that exposure to the isoflavone genestein, with the given dosages, does not impact the matal reproductive health while the high dose brings about masculinization of the pups which implies that isoflavone exerts its action as an endocrine disruptor affecting postnatal development. This could be attributed to the decrease in estrogen due to the inhibition of aromatase, an enzyme involved in estrogen synthesis.