Median lethal dose of Claciferol (Vitamin D) against albino mice Mus musculus was estimated.   Calciferol could be classified as a highly toxic compound to albino mice as its LD₅₀ values to the (immature and adult) were 47 and 60 mg/kg, respectively.  Three doses representing 1/10, 1/20 and 1/30 of the LD₅₀ were administered orally for 2 weeks. In treated animals the rate of body weight gain, water and food consumption were decreased clearly at 1/10 LD₅₀ of  Calciferol than other doses.  Similarly, organs weight/body weight ratio was lower than that observed in non-treated animals. Calcium, phosphorus and cholesterol levels were affected.  The tissue-specific enzymes alkaline phosphates (AP), the amount of urea, creatinine and total proteins of serum, liver and kidney were significantly increased.