Objective: To investigate the association of genetic background between MTHFR C677T genotype and infertile females with polycystic ovarian syndrome. Materials and Methods: We compared 86 infertile females with polycystic ovarian syndrome (PCOS) with 100 healthy fertile females with one or more offspring. Pyrosequencing analysis for MTHFR C677T variation was performed on polymerase chain reaction (PCR) product of study group. To validate pyrosequencing data of C677T variation for randomly selected 50 samples, we compared the pyrosequencing result with the PCR-RFLP (Restriction Fragment Length Polymorphism) result of MTHFR C677T genotype. Results: The prevalence of the C677T mutant homozygous (TT) was significantly lower (p=0.0085) in females with PCOS (8.14%) than in fertile females (21.00%). MTHFR 677 TT genotype had a decreased risk (3.7-fold) of PCOS compared with wild type (MTHFR 677 CC). Conclusion: Our data support a role for MTHFR mutant homozygous (677 TT) genotype in reducing risk in Korean infertile females with Polycystic ovarian syndrome.