The prognosis and overall survival of castration-resistant prostate cancer (CRPC) patients are poor. The search for novel and efficient anti-CRPC agents is therefore extremely important. WM-3835 is a cell-permeable, potent and first-in-class HBO1 (KAT7 or MYST2) inhibitor. Here in primary human prostate cancer cells-derived from CRPC patients, WM-3835 potently inhibited cell viability, proliferation, cell cycle progression and in vitro cell migration. The HBO1 inhibitor provoked apoptosis in the prostate cancer cells. It failed to induce significant cytotoxicity and apoptosis in primary human prostate epithelial cells. shRNA-induced silencing of HBO1 resulted in robust anti-prostate cancer cell activity as well, and adding WM-3835 failed to induce further cytotoxicity in the primary prostate cancer cells. Conversely, ectopic overexpression of HBO1 further augmented primary prostate cancer cell proliferation and migration. WM-3835 inhibited H3-H4 acetylation and downregulated several pro-cancerous genes (CCR2, MYLK, VEGFR2, and OCIAD2) in primary CRPC cells. Importantly, HBO1 mRNA and protein levels are significantly elevated in CRPC tissues and cells. In vivo, daily intraperitoneal injection of WM-3835 potently inhibited pPC-1 xenograft growth in nude mice, and no apparent toxicities detected. Moreover, intratumoral injection of HBO1 shRNA adeno-associated virus (AAV) suppressed the growth of primary prostate cancer xenografts in nude mice. H3-H4 histone acetylation and HBO1-dependent genes (CCR2, MYLK, VEGFR2, and OCIAD2) were remarkably decreased in WM-3835-treated or HBO1-silenced xenograft tissues. Together, targeting HBO1 by WM-3835 robustly inhibits CRPC cell growth.