Vitamins are organic molecules that are required for health, growth and reproduction. Human body is unable to synthesize adequate amounts of vitamins, except vitamin D. Therefore, they should be obtained through diet via foods or supplements. Vitamin deficiencies are generally due to malnutrition, on the other hand, toxicity is usually due to over usage of vitamin supplements. Drug interactions may also effect serum vitamin concentration. For example, anticonvulsant therapy may result in deficiency of folic acid, or proton pump inhibitors may decrease the absorption of Vitamin B12. Vitamins are also important in maintaining the mental health. Vitamin B9 (folate), Vitamin B12 (cobalamine), Vitamin B1 (thiamine), Vitamin B6 (pyridoxine) and vitamin E deficiencies have been known to cause mental dysfunction. Thiamine is essential for pentose-phosphate pathway and oxidative decarboxylation reactions and is important for brain functions. Wernicke’s encephalopathy and Korsakoff’s psychosis caused by thiamine deficiency. Vitamin B2 (riboşavin) is required as a cofactor (FMN and FAD) for many of the enzymes in human metabolism. Pyridoxine has a critical role in synthesis of many neurotransmitters (dopamine, noradrenaline, adrenalin, serotonine, histamine, GABA) associated with mental functions. Decreased levels of pyridoxine are usually seen in alcoholics, which lead to epileptic seizures, EEG abnormalities, depression and confusion. Vitamin B9 (folic acid) plays a basic role in one carbon metabolism and act as a cofactor for serotonin, noradrenaline, dopamine, DNA and phospholipid synthesis. Many of the studies showed that low folic acid levels are associated with mood disorders. Deficiency of Vitamin B12 (cobalamine) causes both neurological and hematological pathologies. Acting as a coenzyme in one-carbon transfer reactions, cobalamine deficiency is highly related to demyelination defects. Folic acid and vitamin B12 deficiencies may result in impaired synthesis of purine and pyrimidine bases. Hematologic findings of vitamin B12 deficiency may be masked by high doses of folic acid ingestion, but this condition will not delay psychiatric symptoms. Vitamin C has also a critical role in biosynthesis of neurotransmitters and it is essential for brain functions. However, association between mental disorders and some of the other vitamins is not well established yet. Further investigations are needed to explain relationship between vitamins and psychiatric disorders.