Background: Folate and vitamin B12 have a number of biologic roles that makethem important in hematological disorders and MALIGNANCY. In the present study, wehave assessed serum folate and vitamin B12 levels and their associated variables inpatients with leukemia, lymphoma, and solid tumors. Methods: This cross-section study investigated 98 patients (57 with leukemia, 16lymphoma, and 25 solid tumors) between April 2015 and March 2016 in Southern Iran. Complete blood counts and serum levels of folate, vitamin B12, lactate dehydrogenase, and homocysteine were measured. Clinical characteristics of the patients were alsogathered from their medical records. Results: Patients had the following mean serum levels: serum folate (12. 27± 6. 69ng/ml), vitamin B12 (331. 81± 183. 22 pg/ml), and homocysteine (11. 74± 26. 67 μ mole/L). Vitamin B12 showed a significant negative correlation with homocysteine levels (r=-0. 223, P=0. 043). Overall, there were 21(21. 9%) vitamin B12 and 9 (9. 8%) folatedeficient patients. Vitamin B12 patients had a longer remission time (time from offtherapy until study entry) of 18± 16. 97 months compared to those with normal vitaminB12 levels (8. 81± 8. 08 months, P=025). However, logistic regression analysis showedthat only mean corpuscular volume had a significant correlation with vitamin B12deficiency (B=-0. 105, odds ratio=0. 9, 95% CI: 0. 819-0. 990, P=0. 03). None of thevariables showed significant correlation with folate deficiency (P>0. 05). Conclusion: Vitamin B12 and folate deficiency are frequently seen in survivors ofCHILDHOOD MALIGNANCY, mainly due to the effects of chemotherapy. These vitamins haveimportant roles in hematopoiesis, as well as development and maintenance of the nervoussystem; therefore, timely detection of their deficiencies is of utmost importance. It ishighly recommended to check the serum levels of these vitamins in children whosuccessfully survive their cancer treatments.