This double-blind, placebo-controlled, one-centered, randomized clinical trial aims to assess the effects of oral calcitriol on oral mucositis in patients undergoing autologous peripheral blood hematopoietic stem cell transplantation. Patients age between 18 and 65 years with Hodgkin’s lymphoma, non-Hodgkin’s lymphoma, or multiple myelomas candidate for autologous hematopoietic stem cell transplantation will be enrolled and patients with baseline serum calcium >10.5mg/dL, phosphorous >4.5mg/dL, renal or liver complications, sensitivity to calcitriol, or disability for oral intake will be excluded. In all, 80 patients will be equally randomized between the calcitriol and placebo groups. Baseline serum levels of 25-OH-D and 1,25-(OH)2-D will be measured before the conditioning regimen. Besides, serum level of 1,25-(OH)2-D will be measured on day 14 after transplantation. Oral calcitriol 0.25mcg or placebo pearls will be administered three times daily after the conditioning regimen up to day 14 after the transplantation. All patients in both groups will receive similar regimen for prevention of oral mucositis according to standard protocol of transplantation ward. Oral mucositis will be check every day up to day 21 after transplantation or up to day recovery of mucositis. Serum calcium and phosphorous will be measured biweekly. Furthermore, liver function test (AST,ALT,AlkP) and Bun, serum Cr will be measured on a weekly and daily basis, respectively. Primary outcomes include the effect of oral Calcitriol on the incidence rate, severity and duration of oral mucositis in patients’ receiving the drug.