Thie paper aims to study the activity and mechanism of synthetic Ruditapes philippinarum oligopeptides(RPO) against prostate cancer DU-145 cells. After being incubated with RPO, DU-145 cells' apoptosis rate, changes in mitochondrial membrane potential, cytochrome C expression, changes of caspase3 and caspase9, cell ultrastructure changes were observed with flow cytometry, laser confocal microscope, Western blotting and electron microscope. The results showed that the factor to induce apoptosis of DU-145 cells is concentration and time dependent, when the RPO concentration was 2.5 mg/mL, the DU-145 cells inhibition rate was 49.9%±4.1% for 24 hours, 97.2%±7.3% for 72 hours. Those DU-145cells incubated with RPO were found to exhibit typical characteristics of apoptosis, such as nucleus psychosis, condensed chromatin, and nucleus fragmentation. The apoptosis rate of DU-145 cells rose as the concentration of RPO increased. Western blotting demonstrated that RPO increased the protein levels of Bax, caspase-3, caspase-9, Cyt-C and reduced the protein expression of Bcl-2. RPO can inhibit the proliferation and induce apoptosis of DU-145 cells possibly by up-regulating expression of Bax, down-regulating the expression of Bcl-2, reducing the Bcl-2/Bax ratio, inducing decline of mitochondrial membrane potential, promoting Cyt-C transfer and stimulating the caspase family cascade reaction.