Abstract: Porphyra haitanesis is an important economic algae with abundant nutrition.To explore the anti- tumor peptides from Porphyra haitanesis,the protein extracted with coalition of repeated freeing and melting and ultrasonic- extraction were hydrolyzed by papain.The obtained proteolytic peptides were separated and purified by ultrafiltration,Sephadex G- 15 and MALDI- TOF- MS,the whole process was guided by MTT method.Results showed that the component P2 which contained 5 peptides purified from papain hydrolysates( called P,molecular weight 0~3 ku) had a strong anti- proliferation effect on both MCF-7 and Hep G-2 cells,the IC50 were 63.64 μg / m L and 59.09 μg / m L,respectively,both which were superior to the positive control 5- fluorouracil( IC50 of MCF-7 and Hep G- 2 were 195.45 μg / m L and 122.72 μg / m L,respectively).While the component P3 which contained 11 peptides also had a certain selective anti- proliferation effect on Hep G-2 cells with an IC50 of 209.09 μg / m L.