AMIS: Hashimoto's thyroiditis (HT) is the most common type of autoimmune thyroiditis and is a risk factor for the occurrence of thyroid papillary carcinoma (PTC). The study aimed to explore the distribution of CARD9 rs4077515 polymorphism in HT and PTC patients, in order to evaluate its association with the occurrence and development of HT.150 HT patients and 120 PTC cases were included. Genotypes of CARD9 rs40775155 polymorphism were sequenced and counted.A remarkable increase trend of rs4077515 AA genotype was found in HT cases in comparison with the control group, while GG genotype frequency exhibited a down trend. An excess of A allele was also detected in HT group. HT cases carrying AG and AA genotypes had high risk to receive hormonotherapy and needed a much larger dose. In comparison with HT cases, both AG and AA appeared more frequently in PTC patients, and are associated with the tumor size, LN metastasis and surgical margin. The AG (OR = 2.566, 95 % CI = 1.376-4.786) and AA (OR = 3.040, 95 % CI = 1.525-6.060) genotype carriers had a greater risk of developing PTC. The A allele of rs4077515 polymorphism was a risk allele for the onset of PTC among HT cases (OR = 1.775, 95 % CI = 1.260-2.502).CARD9 rs4077515 polymorphism is likely to be a risk factor for HT in the Chinese Han population, it also contributes to the development of PTC for HT patients.