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Background & Objective: Aluminum (Al), the 3rd common element in the earth’s crust has a significant toxin potential for humans. Although the knowledge of Al toxicity has markedly improved in recent years, there is relatively little information regarding the embryotoxic and teratogenic potential of Al. the purpose of this study was to assess the effect of short-term exposure of pregnant mice to Aluminum Chloride on the external organ formation of their fetuses. Materials & Methods: Mature NMRI mice (24-33 g) were used in this study. Day 0 of pregnancy defined as the day in which the vaginal plug was found. Plug-positive mice were randomly divided into size groups. The first, second and 3rd groups of animals were given IP injection of single dose of AlCl3 at 150 mg/kg/day on days 10, 11 and 12 of gestation respectively. Mice in the 3 other groups (Controls) received single injection of 0.3 ml saline on days 10, 11 and 12 respectively. Mice were killed on day 15 of gestation. Live fetuses were weighed and examined for external abnormalities. Results: The fetal body weight was significantly reduced in all Al-treated groups (P<0.05). The proportions of external malformations in 10th, 11th and 12th days treated were 47.0%, 37.0% and 33.1% groups respectively with significantly increase comparing to controls (P<0.05). Conclusion: It is concluded that a single dose of the Al administered to pregnant mice can cause external malformations in their fetuses.