This paper has studied the hydrophilizing effect of support on the performance of pressure retarded osmosis(PRO). The hydrophilicity of polyester support has been controlled with cellulose solutions. In order to investigate the effectof hydrophilizing of support, the performance test has been conducted with membrane which compose of active layer andsupport in absence of support layer. The active layer has been made by casting of cellulose tri-acetate (CTA) 1,4-dioxanesolution (13 wt%) and combined with the hydrophilized support. The results show that water fluxes of PRO membraneswith hydrophobic or hydrophilized support were measured 0.8 L/m²hr and 1.2 L/m²hr under 5 kgf/cm²pressure, respectively.However, water flux increase did not accord with hydrophilicity of supports treated by cellulose solutions. It is because the porosity and pore size of supports decrease as the cellulose concentration increases. This result confirms that both the hydrophilizationof support and the maintenance of membrane porosity are important to enhance the performance of PROmembrane.