The glycoprotein of Pinctada martensii was extracted with phosphate buffer in low temprature.The crude extract was then fractionated with 4 concentrations of ammonium sulfate solution.The composition and anti-oxidative property of the fractions were studied.Purified PMGP was prepared from the precipatate at 80%~100% saturation through Sephadex G-75 chromatography.SDS-PAGE and HPLC analysis showed that the PMGP was of high purity,and its molecular weight was about 11.6ku.The content of protein in PMGP was 95.08%,and sugar was 4.92%.It showed strong scavenging efficiency on DPPH radical and superoxide anion radical.