BACKGROUND: The phenotypic switch of vascular smooth muscle cells (VSMCs) underlies the pathology of many cardiovascular diseases. Histone deacetylase 3 (HDAC3) is reported to upregulate in several cardiovascular diseases. RGFP966 is a highly selective HDAC3 inhibitor. This study aimed to explore the effects of RGFP966 on the phenotypic switch of VSMCs. METHOD: First, we conducted an analysis of HDAC3 expression utilizing pertinent Gene Expression Omnibus (GEO) datasets. Then CCK-8, Edu, and wound healing assays were used to explore the effects of RGFP966 on the proliferation and migration of VSMCs and potential mechanisms at the cellular level. RESULTS: Our results showed that palmitic acid (PA) induced the accumulation of lipid droplets in VSMCs, downregulated Adipose triglyceride lipase (ATGL), and increased VSMC viability and migration, which were significantly reversed by RGFP966. Additionally, siRNA targeting ATGL dramatically enhanced the VSMCs injury induced by PA. The autophagy inhibitor 3-Methyladenine (3-MA) partially reversed the decreased ATGL expression caused by PA. Furthermore, the p-mTOR/mTOR ratio decreased under PA induction and rebounded after administration of RGFP966. CONCLUSION: RGFP966 has a protective effect against VSMCs phenotype transitions, potentially related to the regulation of ATGL.