Background: Folate and vitamin B12 have a number of biologic roles that make them important in hematological disorders and malignancy. In the present study, we have assessed serum folate and vitamin B12 levels and their associated variables in patients with leukemia, lymphoma, and solid tumors.Methods: This cross-section study investigated 98 patients (57 with leukemia, 16 lymphoma, 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 also gathered from their medical records.Results: Patients had the following mean serum levels: serum folate (12.27±6.69 ng/ml), vitamin B12 (331.81±183.22 pg/ml), and homocysteine (11.74±26.67 μmole/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%) folate deficient patients. Vitamin B12 patients had a longer remission time (time from off therapy until study entry) of 18±16.97 months compared to those with normal vitamin B12 levels (8.81±8.08 months, P=025). However, logistic regression analysis showed that only mean corpuscular volume had a significant correlation with vitamin B12 deficiency (B= -0.105, odds ratio=0.9, 95% CI: 0.819-0.990, P=0.03). None of the variables showed significant correlation with folate deficiency (P>0.05).Conclusion: Vitamin B12 and folate deficiency are frequently seen in survivors of childhood malignancy, mainly due to the effects of chemotherapy. These vitamins have important roles in hematopoiesis, as well as development and maintenance of the nervous system; therefore, timely detection of their deficiencies is of utmost importance. It is highly recommended to check the serum levels of these vitamins in children who successfully survive their cancer treatments.