This study examined the synergetic effect of class IA Phosphoinositide 3-kinases catalytic subunit p110 beta knockdown in conjunction with oxaliplatin treatment on colon cancer cells. Down-regulation of p110 beta by siRNA interference and oxaliplatin treatment were applied in colon cancer cell lines HT29, SW620 and HCT116. MTT assay was used to measure the inhibitory effect of p110 beta knockdown on the proliferation of colon cancer cell lines. SubG1 assay and Annexin-V FITC/PI double-labeling cytometry were applied to detect cell apoptosis. And cell cycle was evaluated by using PI staining and flow cytometry. The expression of caspase 3, cleaved PARP, p-Akt, T-Akt and p110 beta was determined by western blotting. The results suggested that down-regulation of p110 beta expression by siRNA obviously reduced cell number via accumulation in G(0)-G(1) phase of the cell cycle in the absence of notablely increased apoptosis in colon cancer cell lines HT29 and SW620 (S phase arrest in HCT116). Moreover, inhibition of p110 beta expression increased oxaliplatin-induced cell apoptosis and cell cycle arrest in HT29, HCT116 and SW620 cell lines. In addition, increases of cleaved caspase-3 and cleaved PARP induced by oxaliplatin treatment were determined by immunoblotting in p110 beta knockdown group compared with normal control group and wild-type group. It is concluded that down-regulated expression of p110 beta could inhibit colon cancer cells proliferation and result in increased chemosensitivity of colorectal cancer cells to oxaliplatin through augmentation of oxaliplatin-induced cell apoptosis and cell cycle arrest.