Th e Nanometer TiO 2 powder was put into the unsaturated p olyester resin for the simultaneous mo dification of strength-ening and flexibilizing.The impact strength was used to characterize th e ductility of the nano-TiO 2/UPR.It was found that the resin had the apparent brittleness-ductility t ransition phenomenon,a nd the content of TiO 2 at the brittleness-ductility transition point,was 6wt%.The bending stre ngth and impact strength of the nano-TiO 2/UPR were increased by 55%and 46%respectively compared with those of UPR.The micro observation of the impact fracture i ndicaties that,the fracture pattern of the nano-TiO 2/UPR changes from typical brittleness to typical toughness fracture near th e critical point.