New conjugated random copolymers of poly( p-phenylene benzobisoxazole) (PBO) and poly( 2,5-benzoxazole) (ABPBO) with various compositions have been synthesized and characterized by Fourier transform infrared (FTIR), wide-angle X-ray diffraction (WAXD), UV-absorption, and photoluminescence spectra. The side-to-side distance between two neighboring PBO-ABPBO chains can be modulated by the composition ratio. The absorption, excitation, and emission peaks for the copolymers in methanesulfonic acid can also be regulated by the copolymer composition from the homopolymer ABPBO solution to homopolymer PBO solution. However, the emission peaks of copolymers in solid state are quite different from those of their homopolymers. The copolymers showed blue shifted, structured emission spectra centered with higher quantum efficiency at 470 nm compared with the parent homopolymer PBO, indicating the effects of exciton confinement in the random copolymers. The relationship between the structure and properties for the random copolymers can be interpreted roughly by the sequence length distribution of the different segments estimated from the copolymerization statistics. (C) 2004 Kluwer Academic Publishers.