Purpose. Our aim was to explore whether vitamin A has protective effect on high-dose-methotrexate (HDMTX)-induced intestinal D-xylose malabsorption in children with leukemia and lymphoma. Patients and methods. We performed a prospective randomized unblinded study of vitamin A in 35 children with leukemia and lymphoma who were planned to receive HDMTX 3 g/m(2) and 5 g/m(2), respectively. Twenty-two patients (group 1) received a single dose of 180,000 IU a day before HDMTX was given, and 13 (group 2) received only HDMTX. The vitamin A group received the vitamin only once. Oral D-xylose absorption tests before and 7 days after HDMTX were carried out to evaluate intestinal absorption. Retinol-binding protein (RBP) levels prior to therapy were also measured for vitamin A status. Results. Although we observed no difference of HDMTX-induced toxicity, including hematological, dermatological, systemic, and other toxicities, between groups, the D-xylose absorption test was significantly better in-group 1 (p=0.030). Absorption was decreased in five of 22 patients (23%) who received vitamin A comparing to eight of 13 (62%) who received only HDMTX (p=0.033). RBP levels were lower than normal in 13 of 22 patients in-group 1 and nine of 13 in group 2. In patients whose RBP levels were lower than normal, HDMTX-induced toxicity was lower in the group 1 than group 2 but not statistically significant. No sign of vitamin A toxicity was observed throughout the study. Conclusion. The administration of vitamin A before HDMTX may protect against drug-induced D-xylose malabsorption in children with cancer. Further studies are apparently needed to clarify the full benefits of vitamin A in preventing HDMTX-induced mucosal damage.