According to the World Health Organization (WHO), approximately 890 million people in the world were living with obesity in 2022. In South Korea, the prevalence of obesity has gradually increased, rising from 30.2% to 38.4% (2012–2021).1 Ubiquitin-specific protease 17 (USP17) significantly impacts critical cellular processes, including cell proliferation and oncogenesis.2 However, the role of USP17 in adipogenesis, a key process in obesity development, remains incompletely understood. Here, we investigated the functions of USP17 and the underlying mechanisms in 3T3-L1 adipocyte differentiation. Notably, a remarkable reduction in USP17 expression was observed following the induction of differentiation, largely due to dexamethasone. We then identified USP17 as a negative regulator of adipogenesis, as indicated by reduced lipid accumulation and down-regulation of adipogenic genes. Furthermore, USP17's deubiquitinating activity was indispensable for its regulation of adipocyte differentiation. Moreover, we identified histone deacetylase 1 (HDAC1) as a direct substrate of USP17. By stabilizing HDAC1 through deubiquitination, wild-type USP17, but not the catalytically inactive mutant USP17 (C89S), suppresses the transcriptional activity of peroxisome proliferator-activated receptor gamma (PPARγ). However, HDAC1 was found to partially counteract the resulting increase in PPARγ activity induced by USP17 (C89S). Overall, our findings highlight the potential of USP17 as a promising therapeutic target for obesity therapy.