Abstract: Objective To investigate the effectiveness and safety of endocrine therapy in advanced hormone-receptor-positive breast cancer patients with hypothyroidism. Methods A total of 44 patients with hormone receptor positive breast cancer who were admitted to the Affiliated Hospital of Xuzhou Medical University were enrolled. According to their thyroid function, they were divided into two groups: a normal thyroid function group (n=29) and a hypothyroidism group (n=15). The progression free survival (PFS), thyroid function (FT3, FT4 and TSH), breast cancer markers (CEA, CA125 and CA15-3) and adverse reactions were retrospectively analyzed. Results There was no statistical difference in ORR between the normal thyroid function group and the hypothyroidism group (P>0.05). The median PFS of the hypothyroidism group (7.5 months) was slightly higher than that of the normal thyroid function group (6.1 months), without statistical difference (P>0.05). There was no statistical significance in the incidence of leukopenia, thrombocytopenia, albumin and abnormal liver function between the two groups (P>0.05). After two cycles of treatment, there was no statistical difference in thyroid function compared with those before treatment (P>0.05). There was no statistical difference in CEA, CA125 and CA15-3 between the two groups before and before treatment (P>0.05). Conclusions The use of endocrine therapy for advanced breast cancer patients with hypothyroidism exerts similar effect with those normal thyroid function, with almost the same incidence of adverse reactions and good tolerance.