Introduction & Objective: Mental retardation is a disorder in people under 18, accompanied with restriction in mental abilities, daily activities, and social skills. These patients are at risk of malnutrition. The objective of this study is assessment of folic acid, vitamin B12 and some of the interactive factors in mentally retarded patients.Materials & Methods: This descriptive study was conducted in 40 subjects 7-15 years old, which were divided into two groups: girls (n=20) and boys (n=20). 24 hours dietary recall for two consecutive days and food frequency questionnaire (ffq) were used to evaluate intake of folate and vitamin B12. RIDA method was used for measurement of serum folate and vitamin B12 with siwul- tral- SNB-Radioassay kit. Chi square and independent T-test and Spearman and Mann- Whitney also were used to compare groups.Results: The results of this study showed that folate and vitamin B12 intakes, were lower than RDA in all subjects. Meanwhile serum folate, erythrocyte folate and serum vitamin B12 were low in 65, 62.5 and 35 percent of subjects, respectively. Mean (±SD) of serum folate, vitamin B12 and erythrocyte folate levels were 2.89 and 3.11 (ng/ml), 274.5 and 327.75 (pg/ml) and finally 98.26 and 103.27 (ng/ml) in girls and boys, respectively. Serum folate level correlated positively with vegetables consumption (p<0.05, r= 0.87). Erythrocyte folate levels correlated negatively with anticonvulsant drugs consumption (p=0.01, r=-0.66), and parasite evidence (p=0.01, r=-0.82) and correlated positively with vegetables consumption (p<0.05, r=0.22). Finally, serum vitamin B12 level correlated negatively with anticonvulsant drugs consumption (p=0.01, r=-0.46) and parasite evidence (p<0.05, r=-0.60) and correlated positively with meat consumption (p=0.01, r=0.42).Conclusion: The status of folate and vitamin B12 in these mental retarded patients was not sufficient due to both low intake and parasite evidence and finally anticonvulsant drug consumption.