The mechanical property and fracture morphology of glass fiber- (GF) and carbon fiber-(CF) reinforced polysulfone (PSF) blends with bis (4-(4-ethynyl phenoxy) phenyl) sulfone (ATS-C) have been investigated. Experimental results show that the tensile and flexural properties and impact strength of GF-reinforced ATS-C/PSF composites decrease as the processing temperature or/and the processing time increase, but CF-reinforced ATS-C/PSF composites exhibit better mechanical properties. Although interlaminar shear strength (ILSS) for fiber-reinforced ATS-C/PSF composites decreases, scanning electron microscopy (SEM) observation of fracture surface indicates that the fractural model of fiber-reinforced PSF composites changes from the interfacial debonding fracture to the matrix fracture at the interfacial region with addition of ATS-C and the increase of the processing temperature. The end-use temperature of polysulfone can be retained and solvent resistance of polysulfone can be improved due to the formation of a semi-interpenetrating polymer network.