In this paper, a novel polyimide with trifluoromethyl group (PIS) was synthesized successfully and used toimprove the toughness of epoxy resins. Five modified epoxy resins (5, 7.5, 10, 12.5 and 15 wt%) were prepared andinvestigated, respectively. The structure, thermal properties, tensile properties, viscoelastic properties, toughness andmorphology of modified epoxy resins were studied by Fourier Transform Infrared Spectroscopy (FT-IR), thermogravimetricanalysis (TGA), Instron 5967, Dynamic Mechanical Analysis (DMA), and Scanning Electron Microscopy (SEM). Theresults showed that the epoxy resins modified with PIS exhibited good thermal stability which the glass transitiontemperatures increased from 135.9 oC to 146.4 oC. Tensile strength of modified epoxy resins increased from 40.4 MPa to92.3 MPa. The KIC values increased from 0.86 MPa·m1/2 to 1.56 MPa·m1/2 indicated that the toughness enhancement wasmarkedly. The fracture modes also were examined by SEM images and exhibited the fracture mode changed from the brittleone to ductile fracture with varied weight of the novel trifluoromethyl-polyimide.