Esterification of polysaccharide had been carried out by catalysis using a series of catalysts, which were synthesized by H3PW12O40 (HPW) immobilized on chloromethylated polystyrene bead (PSC) and named as PS-EDA-HPW, PS-DETA-HPW, PS-TETA-HPW and PS-(AST-HPW)(n) according to different linker in the reaction system. The catalysts were characterized by FTIR spectroscopy, nitrogen adsorption, X-ray diffraction and inductively coupled plasma atomic emission spectrophotometer. PS-(AST-HPW)(n) showed the highest efficacy on esterification of polysaccharide. Four phosphorylated derivatives (POP1-p) of a native polysaccharide (POP1) from Portulaca oleracea L with different degree of substitution (DSp) were obtained using PS-(AST-HPW)(n) as the catalyst. Chemical equilibrium was established as quickly as 10 h with the content of P more than 5%. Compared with native POP1, POP1-p exhibited superior antioxidant activities in vitro, which indicated that phosphorylated modification could enhance antioxidant activities of POP1. It was obvious that the DSp had a significant effect on the antioxidant activity. (C) 2011 Elsevier B.V. All rights reserved.