OBJECTIVES: Recently in schizophrenia high incidence of MTHFR(methylenetetrahydrofolate reductase), which is a main relating enzyme that reduce homocysteine level, genetic variations were reported. So we examined serum homocysteine level and MTHFR gene polymorphism in Korean schizophrenics. METHOD: We compared serum homocysteine level and MTHFR polymorphism between 235 schizophrenics (100male, 135female) and 235 normal controls(100male, 135female). C677T and A1298C polymorphism of MTHFR gene were analyzed. RESULTS: 1) C677T genetic mutation(CT and TT) were more frequent in schizophrenia group than normal control group(p<0.01). But the difference of A1298C mutation frequency was not found between two groups. 2) In schizophrenia patients, TT genotype of C677T mutation showed significantly higher homocysteine level (29.99uM/L) than other group(CT : 13.34uM/L, CC : 9.34uM/L p<0.01). 3) MTHFR 677 TT homogeneous mutation genotype showed two times more risk(odds ratio=2.15) than 677CC normal genotype in schizophrenia. CONCLUSION: Some schizophrenia patients with high homocysteine serum level may have C677T TT genotype. In that case, folate ingestion could be a good management for clinical improvement.