The toxic and teratogenic effects of lyophilized water extracts of Ocimum sanctum and Tamarindus indica in Danio rerio embryos and their active phytochemicals were assessed and analyzed in this study. Analysis revealed that O. sanctum contained flavonoids, terpenoids, saponins, and tannins while T. indica had flavonoids, terpenoids, saponins, and alkaloids. In D. rerio assay, a 100% mortality was observed in embryos exposed to 5000 ppm and 10000 ppm of O. sanctum and to 10000 ppm of T. indica after 12 hours of exposure. At 48 hours of exposure, O. sanctum extract-treated embryos showed 25.00% and 58.33% mortality while T. indica had 8.33% and 33.33% mortality at 100 and 500 ppm concentrations of each extract, respectively. Embryos at 100 ppm or higher concentrations significantly recorded lower heartbeat rate while no heartbeat was observed in embryos at 1000 ppm or higher concentrations of O. sanctum and at 5000 ppm or higher concentrations of T. indica. Embryos exposed to 100 ppm and 500 ppm significantly recorded lower hatchabilities (66.67% and 16.67% for O. sanctum and 91.67% and 58.33% for T. indica, respectively) when compared to the control embryos. No hatched was noted in 1000 ppm of both plant extracts. Growth retardation, yolk deformity, and tail malformation were the most observed teratogenic effects of both plant extracts.