Abstract: Polyimide (PI) sizing of carbon fibers (CFs) was performed by coating them with polyamic acid synthesized from pyromellitic dianhydride and 4,4'-oxydianiline, followed by thermal imidization to improve their interfacial strength with polyphenylene sulfide (PPS) in CF/PPS composites. The surface morphology and chemical structures of the PI-sized CFs were characterized by SEM and XPS, respectively. Results indicated that a continuous and uniform PI sizing layer was formed on the surface of the CFs. The number of carbon atoms bonded to nitrogen and oxygen were increased by 9.72% for the PI-sized CFs compared with the as-received CFs. The interlaminar shear strength, the axial compression strength and axial compression modulus of the PI-sized CF/PPS laminated composite increased by 26.39, 26.02 and 19.64%, respectively compared with the composite without PI sizing.