Genistein is the major phytoestrogen present in soybean and soy-products, which is widely in aquafeed. Genistein content of defatted soybean meal was estimated to be 23.35±1.09 mg/100g. A 56 days experiment was conducted to evaluate the impact of feeding genistein on vitellogenesis and steroidogenesis in female common carp. six months old female fishes were fed with graded level of genistein at 0 (Gen-0), 1 (Gen-1), 3 (Gen-3), 6 (Gen-6) and 9 (Gen-9) mg/ 100 g of feed, which is equivalent to around 0, 4.5, 13.5, 27 and 40.5% inclusion of defatted soybean meal. The number of vitellogenic oocytes in the ovary and serum vitellogenin level were significantly decreased in genistein-fed fishes compared control whereas serum estradiol and cholesterol contents were significantly higher (P<0.05) in Gen-9 group, whereas cortisol level was significantly higher in Gen-6 and Gen-9 groups. Genistein induced U-shaped response in serum progesterone (y = 0.1217x2 - 0.6452x + 1.141, R2= 0.9388) and testosterone (y = 0.2168x2 - 0.8912x + 2.0868, R2=0.6538) level. The study revealed that structural resemblance of genistein to animal estrogen may have led to compete with 17-β estradiol for binding to estrogen receptors of the liver, that impaired vitellogenin synthesis and hence creates steroid imbalance during ovarian growth of common carps. Genistein at 1mg/100g of feed had negatively affected vitellogenesis which presumes that even inclusion of soybean at 4.5% (1mg% equivalent genistein) may affect the vitellogenesis and hence needs further research.