Little is known about how health insurance policies, particularly in developing countries, influence breast cancer prognosis. Here, we examined the association between individual health insurance and breast cancer-specific mortality in China. We included 7436 women diagnosed with invasive breast cancer between 2009 and 2016, at West China Hospital, Sichuan University. The health insurance plan of patient was classified as either urban or rural schemes and was also categorized as reimbursement rate (ie, the covered/ total charge) below or above the median. Breast cancer-specific mortality was the primary outcome. Using Cox proportional hazards models, we calculated hazard ratios (HRs) for cancer-specific mortality, contrasting rates among patients with a rural insurance scheme or low reimbursement rate to that of those with an urban insurance scheme or high reimbursement rate, respectively. During a median follow-up of 3.1 years, we identified 326 deaths due to breast cancer. Compared with patients covered by urban insurance schemes, patients covered by rural insurance schemes had a 29% increased cancer-specific mortality (95% CI 0% to 65%) after adjusting for demographics, tumor characteristics, and treatment modes. Reimbursement rate below the median was associated with a 42% increased rate of cancer-specific mortality (95% CI 11% to 82%). Every 10% increase in the reimbursement rate is associated with a 7% (95% CI 2% to 12%) reduction in cancer-specific mortality risk, particularly in patients covered by rural insurance Schemes (26%, 95% CI 9% to 39%). Our findings suggest that under-insured patients face a higher risk of breast cancer-specific mortality in developing countries. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.