The incidence of acute rejection has declined dramatically as a result of new immunosuppressive medication. Unfortunately, some of these drugs have important metabolic side effects. Recently, it has been shown that new immunomodulator drugs have potential advantages on rejection prevention without any side effects. Calciteriol is now believed to play a role in the immune responses both in vitro and in vivo. This study was aimed to compare the rate of acute rejection and its effects on metabolic consequences between patients receiving and those not receiving calciteriol. Fifty patients undergoing renal transplantation from living donors were randomized into a prospective controlled trial. They were divided into two groups and all of them received prednisolone, cyclosporine and mycophenolate mofetil. One group (C+) was treated with calciteriol for six months. They were matched for age of recipients and donors, recipient-donor relationship, underlying diseases, length of hemodialysis and panel reactivity test status. While C+ group received less cyclosporine, the incidence of acute rejection was similar in both groups. They received 4.9 +/- 0.7 mg/kg and 2.32 +/- 0.9 mg/kg of cyclosporine at the end of first and sixth months respectively while the control group received 5.4 +/- 1.3 mg/kg and 3.75+/- 0.9 mg/kg (p value=0.08 and p value=0.09). No significant difference between two groups was observed on serum calcium, phosphorous, lipid profile and infection rate. This study indicates that calcitriol without having any significant side effect is useful for prevention of acute rejection when added to an immunosuppressive regimen.