The main purpose of this research project was to investigate the teratogenic effects of the thiamethoxam (TMX) on the development of chick embryo. A total of 100 fertilized eggs (72 hours old) of commercial broiler (Ross) were obtained and equally divided into five groups (A to E). The group A and B were kept as negative control and sham control, respectively. The experimental groups were administered with increasing concentrations of thiamethoxam at a dose rate of 50μg, 100μg, and 150μg each diluted in 20μl distilled water. The sham group was treated with 20μl of normal saline. After that, the eggs were incubated under standard conditions. The eggs were opened on day 20^th for the evaluation of any gross anomalies and musculoskeletal deformations. The mortality rate increased gradually with the dosage of TMX. The results showed significant growth retardment in the treated chicken embryos which were further endorsed by lower body weight and reduced crown-rump length. Furthermore, the observed teratogenic effects were deformed head (exencephaly), beak agnathia, anophthalmia, scantiness of feathers, limb deformities, and failed retraction of the yolk sac. Gross and histopathological analysis of vital organs showed remarkable alterations as compared to the control group. It has been concluded that chick embryos exposed to TMX in early embryonic stages showed results in growth retardation at lower dosage, while at higher dosage marked teratogenic and histopathological effects have been recorded in liver.