A series of organ-soluble copolyimides (co-PIs) were synthesized from 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 2,2'-bis(trifluoromethyl)-4, 4'-diaminobiphenyl (TFMB), and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) via a one-step polymerization in N-methyl-2-pyrrolidone (NMP). The polyimide solutions were used to fabricate as-spun polyimide fiber by a wet-spinning process. SEM images of the round cross-section of the fibers indicated that a homogeneous and dense fibrous structure was produced in the coagulation bath of H2O/NMP = 90/10 (v/v) and many microfibrils appeared on the surface. The drawn fibers exhibit excellent mechanical properties, and the strength and modulus of BTDA/TFMB/BIA co-PI fibers (TFMB/BIA = 50/50) reached 2.25 and 102 GPa with a draw ratio of 3.0. The 5 % weight loss temperature of the co-PI fibers in thermogravimetric analysis spectra achieved 548-563 A degrees C in an air atmosphere. The glass transition temperatures were found to be between 340 and 366 A degrees C according to the DMA results. Annealed BTDA/TFMB/BIA co-PI fibers displayed distinct wide-angle X-ray patterns, and crystallinity and crystal orientation with various draw ratios were observed.