Objective: An aberrant immunologic mechanism has been suggested to be involved in the pathogenesis of endometriosis. Vitamin D may be involved in immune response. Vitamin D binding protein (VDBP) mediate the biological effects of vitamin D in humans. The gene encoding VDBP, GC gene, is highly polymorphic. The present study aimed to investigate whether the VDBP gene polymorphisms may be genetic factors for endometriosis in Korean women. Methods: This prospective study of women with endometriosis (n=16) and controls (n=16). Measurements of serum total 25(OH) vitamin D concentrations were performed using the Elecsys Vitamin D Total Kit with the Cobas e602 module; this is an electrochemiluminescent assay with ruthenium-labeled DBP, biotin-labeled vitamin D, and streptavidin-coated microparticles. The levels of bioavailable 25(OH) vitamin D were calculated. DNA was extracted from all samples using a DNeasy Blood & Tissue Kit (250) (Qiagen, Hilden, Germany), following the manufacturers instructions. Concentrations of VDBP were measured by using Human Vitamin D BP Quantikine ELISA kit (R&D Systems, Minneapolis, MN, USA). Two SNPs (rs4588, and rs7041) of VDBP were analyzed with real-time PCR method using TaqMan SNP Genotyping Assay kit. The functional variant of VDBP was determined by the results of two SNPs. Results: Gravidarum and parity in the endometriosis group were statistically significantly lower than in the control group. Serum CA-125 and ESR in the endometriosis group were statistically significantly higher than in the control group. Serum total 25(OH) vitamin D in the endometriosis group was significantly lower than in the control group. However, serum bioavailable 25(OH) vitamin D, Free 25(OH) vitamin D and VDBP did not differ between control and endometriosis groups. Genotype and allele frequencies of VDBP between control and endometriosis did not indicate statistically significance. Conclusion: Korean women with endometriosis had lower serum total 25(OH) vitamin D concentration compared to controls. Serum VDBP concentration and VDBP gene polymorphisms were not associated with endometriosis. Further studies are needed to investigate the pathophysiology and clinical implications of 25(OH) vitamin D and VDBP in endometriosis.