The teratogenicity of commercial formulation of synthetic pyrethroids in chick embryo was evaluated. Fertilized eggs of Gallus domesticus were incubated for 6 days at 37° C. The eggs are divided into 8 batches, having 10 eggs in each batch. With the help of insulin syringe, 1 ml in each egg with following strength in each batch respectively, 0.0025mg/ml, 0.005 mg/ml, 0.0075 mg/ml, 0.01mg/ml, 0.0124mg/ml, 0.0175mg/ml, 0.025mg/ml of synthetic pyrethroid (Transflurithrin) was injected in the vegetal pole of the eggs. The synthetic pyrethroid was dissolved in normal saline. The dose was much less than the commercial formulation which is 8.8mg/ml, used as mosquito repellant. The control was injected with 1ml normal saline. After 14 days, recovered embryos were evaluated for mortality rate, wet body weight and gross morphological malfunction. The result revealed that embryonic mortality markedly increased with the quantity of pyrethroid. This experiment also shows 100%mortality of developing chick embryo in 0.025mg/ml dose. The significant decrease in wet body weight and significant increase in percentage of abnormal survivor was observed in dose dependent manner. Megalocephaly, exencephaly, sometimes twisted neck, low bone density were seen among survivor. The growth and development of digits also hampered. Reddish patch was seen all over the body of developing embryo. Parrot like beak, blunt beak was observed. An overview of external malfunction is seen by pyrethroid treated embryos. These finding suggests that synthetic pyerethroid exhibit embryotoxic and teratogenic effects in developing chick embryo.