The study aimed to investigate the mechanism of the peptide from yellow croaker swim bladder inducing apoptosis in prostate cancer DU-145 cells. Isolation and purification of the peptides from the enzymatic hydrolysate of yellow croaker swim bladder and identification of its amino acid sequences. The CCK-8 method was used to measure the inhibition rate of swim bladder peptide after treatment with YCSB-1c. AO/EB method was used to determine apoptosis in DU-145 cells. Flow cytometry was used to determine apoptosis rate and cell cycle in DU-145 cells， and western blot was used to determine the expression levels of apoptosis-related proteins. The results showed that the YCSB-1c contains two oligopeptides， Ser-Pro-Ser-Pro and Gly-Pro-Ala-Arg. Compared with the control group， the apoptotic cells in the YCSB-1c groups were significantly increased in a dose-dependent manner. Flow cytometry results showed that live cells in YCSB-1c groups were significantly decreased， while the late apoptotic cells were significantly increased. YCSB-1c blocked the cell cycle of DU-145 cells in G0/G1 phase， up-regulated the protein expression of Bax， Caspase-3 and Caspase-9， and induced DU-145 cells apoptosis. YCSB-1c could effectively induce apoptosis in DU-145 cells， and the underlying mechanism is related to cell cycle block and mitochondria-mediated apoptotic pathway.