This study focuses to evaluate the toxicological effects of phytochemical constituents of seed oil extract of Ricinus communis on Nile tilapia. Phytochemical constituents of oil extracted from the seed of mature Ricinus communis plants were screened. Sexually mature female Nile tilapia were oral gavage the seed oil at sub-lethal doses of 1,000mg/kg, 1250mg/kg and 1,500mg/kg body weight and observed for 72 hours post-treatment. Each treatment group was replicated three times. Histological microtome sectioning and staining was carried out to aid microscopic examination of hepatic and ovarian tissues. Increase in the number of rodlet cells and distortion of the vein walls in the fish hepatic tissues were observed with increase in the sublethal concentrations of the seed oil extract, while mild to severe necrosis and granulation of the interstitial tissues were observed in the ovarian tissues as the concentration of the seed oil extract increased from 1000 to 1,500mg/kg. Changes in the liver’s histology revealed mild sub-lethal toxicity effect of R. communis seed oil at moderate level of inclusions. Severe alterations in the ovarian architecture probably denote the antifertility potency of R. communis seed oil linked to the presence of steroids