Various surface modification methods has been applied to improve the antifonling properties of hydrophobic membrane.The common problems faced by some modification methods were pore blocking [1-3],deteriorate of the membrane properties [2],and modification on the membrane surface only then inside membrane pores is still susceptible to fouling [4].In this work,we propose a new strategy for surface modification of a hydrophobic membrane using liquid carbon dioxide (1-CO2) as a coating solvent.The low surface tension and the low viscosity owned by 1-CO2 leads to the formation of uniform and thin coatings of hydrophilic species onto highly porous membranes like PVDF (polyvinylidene fluoride).Polyethylene glycol diacrylate (PEGDA) is used as 1-CO2 soluble hydrophilic monomer source and azobisisobutyronitrile (AlBN) was used as a radical initiator.The modified membranes were characterized using FTIR,XPS,SEM,EPMA and EDX analysis.The sequences of flux experiments using dead end filtration cell were conducted to test the performance of modified membrane.The results are compared with pristine PVDF and Millipore hydrophilic PVDF.The FTIR and XPS spectra showed that PEGDA has been coated on the surface of the membrane.The depth profiling conducted using EPMA showed that the PVDF coated with 1 wt% PEGDA had uniform oxygen concentration at the value of around 2 wt%.While the depth profiling using EDX analysis showed that oxygen concentration inside the membrane pores was uniform and even had higher concentration than that of commercial hydrophilic PVDF.The EDX result is shown in figure 1.The flux experiment showed that in the presence of 1 g/L of Bovine serum albumin (BSA),the flux of our modified membranes were higher than those of the pristine PVDF and the commercial hydrophilic PVDF.This result was agreed well with EDX analysis,which shows that the 1-CO2 based coating has successfully modified not only the membrane surface but also pores of the pristine PVDF membrane.As a result,the modified membrane using 1-CO2 had high resistant to biofouling.