Abstract: Objective:To study anti-tumor activities of the glycosaminoglycan extracted from Pinctada martensii Dunder. Methods:MTT assay was used to determine the inhibition effects of the glycosaminoglycan called PGI and PGII extracted from Pinctada martensii Dunder on proliferation of human Hela cell, L1210 cell and K562cell in vitro, and the ratio of extending viability on the L1210 tumor- bearing mouse caused by the glycosaminoglycan extracted from Pinctada martensii Dunder was examined in vivo. Results:MTT showed that all the PGI and the PGII inhibited the growth of human Hela cell, L1210 cell and K562 cell remarkably in a dose of 25¹00μg·mL-1. The strongest inhibitory effect of the PGI and the PGII was on L1210 cell at the dose of100μg·mL-1, and the maximum inhibitory ratio were 48.2% and 40.4% respectively. PGII combination with chemotherapeutic drug (5-Fu or DDP) can sensitize chemotherapeutic drugs on the HeLa and L1210 tumor. In this paper the life prolongation effect on the L1210 tumor-bearing mouse of the glycosaminoglycan had been proved, the survival prolongation rate of the 100mg·kg-1dosage groups was 19.3% in our experiment.