PurposeThis study aimed to investigate the association between serum cholesterol and triglyceride levels and breast cancer risk in Japanese women.MethodsWe retrospectively evaluated the association between the levels of low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TGs) and the incidence of breast cancer in a cohort study by using the health insurance claims and health checkup data from a database provided by JMDC Inc. We included 956,390 women who were insured between April 2008 and June 2019, identified breast cancer cases by using validated definitions, and estimated the risk of breast cancer by using multivariable Cox proportional hazards regression models adjusted for potential confounders.ResultsDuring the 2,832,277 person-years observation period (median 2.4 years), 6284 participants were diagnosed with breast cancer. There was marginally significant association between LDL-C and breast cancer risk when comparing the highest and lowest quintiles and at the clinical cutoff values for diagnosing hyperlipidemia. HDL-C was not associated with breast cancer. However, when stratified by age groups (< 50 and ≥ 50), HDL-C was inversely associated with breast cancer risk in women over 50 years old. TG was not associated with breast cancer risk.ConclusionIn this population, there was a modest association of LDL-C at the clinical cutoff values for diagnosing hyperlipidemia (140 mg/mL), and there were no associations of HDL-C and TG with breast cancer risk.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10549-023-06917-z.