Osteosarcoma (OS) is an aggressive malignant tumor of bone, which often occurs in children and adolescents. Currently, the effective method for the treatment of OS is still limited. The study aimed to investigate the synergistic antitumor effect of inositol polyphosphate-4-phosphatase, type-II (INPP4B) and rucaparib on OS cells. The expression levels of INPP4B in OS tissues and OS cell lines were examined by quantitative real-time polymerase chain reaction and Western blot analysis. SaOS2 and U2OS cells were then transfected with overexpression vector of INPP4B or were treated with different concentrations of rucaparib, and cell viability, cell cycle, and apoptosis were determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and flow cytometry. Western blot assay uncovered the combined effects of INPP4B and rucaparib on cell cycle, apoptosis and phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) signal pathway. Further, the tumor formation was examined in vivo. Results showed that INPP4B was low expressed in OS tissues and in OS cell lines. INPP4B overexpression significantly decreased cell viability and induced apoptosis in SaOS2 and U2OS cells. Additionally, rucaparib remarkably reduced cell viability in a dose-dependent and time-dependent manner. Meanwhile, rucaparib suppressed cell cycle progression in the S phase and promoted apoptosis in a dose-dependent manner. Further, combination of INPP4B overexpression and rucaparib declined Myc, cyclin E1 and cyclin D1 expressions, enhanced Bad, Bax, and cleaved-caspase-3 expressions, and blocked PI3K/AKT signal pathway in SaOS2 and U2OS cells. Finally, combination of INPP4B overexpression and rucaparib inhibited tumor formation in vivo. The study demonstrated that INPP4B and rucaparib exhibited synergistic antitumor effect by regulating PI3K/AKT pathway in OS cells.