Abstract: Post estrus hypocalcemia is a very rare and exclusive syndrome in the dairy cows that occurs after ending the estrus signs. The aim of this study was introducing the estrus as a rare cause of hypocalcemia in the cow. On the September 2005, an adult half-breed Holstein cow, with symptoms of recumbency, hypothermia and depression was referred to veterinary clinic of the Tabriz University. According to the owner, this case had vigorous estrus signs, the day before the examination and had a history of repeat breeding. After general examination and blood sampling from the jugular vein, post estrus hypocalcemia was confirmed (total serum calcium <5 mg dL ¹). For treatment, 1 L of calcium borogluconate 40% solution was administered intravenously to the cow. After infusion of calcium solution, cow stood up and recovered her health.