Objective To investigate the toxicities of methotrexate in the treatment of the children with acute lymphoblastic leukemia Method 28 children with acute lymphoblastic leukemia were randomly divided into two groups(A and B), they were treated with methotrexate 3.0 g/m 2 (n=16) and 5.0 g/m 2(n=12). The toxicities of two doses of methotrexate were observed. Results The main toxicities of methotrexate were marrow suppression,gastrointestinal reaction and liver damage. They were mostly mild.No statistically significant difference was found between group A and group B .Conclusion The toxicities of methotrexate are common and can be tolerated.