Yttrium-90 (⁹⁰Y) selective internal radiation therapy (SIRT) is an emerging modality for the treatment of hepatocellular carcinoma (HCC), leveraging the nuclide ⁹⁰Y to deliver targeted radiation therapy. ⁹⁰Y has a long half-life and can be used to selectively ablate tumor cells by high-energy beta rays. It has high biological effectiveness and robust local control capabilities. In recent years, with the continuous advancement of basic and clinical research, the application of ⁹⁰Y-SIRT in the conversion treatment of unresectable HCC (uHCC) has made significant progress. However, challenges remain in the clinical application of ⁹⁰Y-SIRT, including how to improve the efficacy of conversion therapy and how to optimize therapy regimens. This review aims to summarize the research progress of ⁹⁰Y-SIRT in the conversion therapy of uHCC.