FCGR2C gene was investigated at first time in Hashimoto disease. The aim of this study is to show with genotype-phenotype correlation analysis of the clinical phenotypic role in autoimmune disease of Hashimoto's thyroiditis of nucleotide polymorphisms or variations in the nature of mutations in FcGR2C gene, responsible for the production of proteins which have an extremely active role in immune system. The study group comprised by 48 patients admitted to Department of Endokrinology of Ege Univercity Faculty of Medicine, Department of Internal Medicine and corresponding to Hoshimoto disease criteries. Also, 25 healthy individuals not diagnosed with Hashimoto thyroid and family history of this disease aggred to participate in the study was included in this study. Looking to the results of this study after analysis of the entire coding region of FCGR2C there was found 12 new mutations. This is 7 mises mutations, 5 sininim aminoacit and also in intron 6 pieces nucleotide was seen. Looking to regions where was found mutations and polymorphisms in this study: Pro83Gln, Pro83Pro, Gln57Gln, Gln63Gln FCGR2C proteins are correspond to the first domain. Mutations and polymorphisms are correspending to second domaine of FCGR2C are Ile183Met, Ser189Thr, Tyr205Phe, Gln57Gln, Gln63Gln, Leu150Leu, Thr203Thr ve Leu204Leu. Furthermore, the frequency of mutant alleles of FCGR2C gene were; %90 in patients group and %70 in healthy control group. After applied for the statistical analysis FCGR2C gene mutations increased significantly (χ2: 10.559 - p: 0.001) in Hashimoto disease patients.