Abstract Objective The aim of this article is to evaluate the cost-effectiveness of abemaciclib plus endocrine therapy (ABE + ET) vs. ET as adjuvant treatment for high-risk hormone receptor-positive and human epidermal growth factor receptor 2-negative (HR+/HER2–) early breast cancer in China. Methods From the perspective of the Chinese health care system, a 5-state Markov model was developed with a lifetime horizon. Data of the monarchE phase III clinical trial were used to model the invasive disease-free survival (iDFS) and standard parameters models were used for data extrapolation. Costs were obtained from national data sources, expert opinions and published literature using 2023 US dollars and discounted by 5%. The results were evaluated in terms of life-years (LYs) and quality-adjusted life-years (QALYs). Sensitivity analyses and scenario analyses were performed to test the robustness of the basic results. Results In the base-case analysis result, the model projected improved outcomes (by 0.65 LYs and 0.72 QALYs) and increased costs (by $16,057.72) for incremental cost-effectiveness ratios (ICERs) of $24,841/LY and $22,385/QALY for ABE + ET vs. ET patients. The results in scenario analysis estimated the ICERs of ABE + ET treatment to be $16,959/LY and $15,264/QALY in a mixture cure model, and $13,560/LY and $12,191/QALY in a non-mixture cure model. The model was sensitive to outcome discount rate and utility of iDFS. Conclusion ABE + ET might not have an economic advantage over ET at a willingness-to-pay (WTP) threshold of one time the per capita GDP in China, but was expected to be more cost-effective at a WTP threshold of three times the per capita GDP. Further analysis will be conducted once data from longer-term studies become available.