Introduction: Arsenic is a standout amongst the most lethal metals derived from the natural environment. The major reason for human arsenic toxicity is tainting of drinking water. Arsenic trioxide is inorganic arsenic that is classified by the US Environmental Protection Agency as a known human carcinogen. Aim: Illustration of morphological and histological effects of arsenic trioxide during mice embryonic development. Methods: Adult female albino mice were divided into five groups: Control, negative control treated with Hcl (arsenic trioxide solvent), and three groups daily treated orally with different doses of arsenic trioxide (0.3, 0.7 and 1 mg/kg). Embryos were morphologically examined, weighed and morphometric measurements were carried out. Embryonic liver and kidney were histopathologically examined. Results: Data showed a significant decrease in body weight and crown rump length in the arsenic high dose group and a significant decrease in head circumference, thigh and a significant increase in foot of all treated groups. Statistics revealed a significant increase in tail measurements with the lowest dose, while the higher doses showed a significant decrease. Severe degenerative histopathological changes in different treatments were also observed. Discussion: Exposure of mice embryos to arsenic trioxide before and during pregnancy-induced morphological and histological abnormalities. It is suggested that the inhibitory effects of arsenic trioxide on embryonic development and body measurement might be attributed to elevating proapoptotic and decreasing antiapoptotic gene activity. The increase of foot and tail measurements in some cases might be explained as a result of increased proliferation rate and mutation in developing systems.