A polysulfone (PSI) self-standing nanofilm was designed for forward osmosis (FO) via the solvent evaporation method and doping sulfonated polysulfone (SPSf) from 0 to 5 wt% to tune the structure and surface property of the nanofilm. The separation performance of the nanofilm was investigated in hydraulic and osmotic pressure driven processes. The experimental results showed that attributed to the formation of interconnected SPSf network in the PSf matrix, the pore size distribution of the PSf self-standing nanofilm narrowed down at the optimized SPSf content of 1 wt%, above which SPSf aggregation occurred and the pore size distribution became broadened. Moreover, by doping SPSf, a more hydrophilic and negatively charged surface was obtained. At the SPSf content of 1 wt%, the rejection of the nanofilm to Na2SO4 increased from 82.0% to 90.8% and the water flux was improved from 0.15 to 0.17 L m(-2) h(-1) in the pressure driven process. Correspondingly, the thinnest nanofilm with the thickness of 46 nm has a highest water flux of 46.4 L m(-2) h(-1) in the FO process using 1.25 mol L-1 Na2SO4 as the draw solution. Such a self-standing nanofilm provides a new approach to develop high performance FO membranes.