Abstract: Multiwalled carbon nanotubes/poly (p-phenylene benzobisoxazole) (MWNTs/PBO) composites was prepared by solution blending in MSA solvent. The microstructures of MWNTs/PBO composites were characterized with SEM. The electrical, mechanical and thermal resistance properties of the composites before and after heat treatment were studied. The results show that MWNTs are dispersed uniformly in PBO matrix, and form a network microstructure that can be improved by heat treatment. Compared to MWNTs/PBO composites before heat treatment, the electrical and mechanical properties of the composites after heat treatment are enhanced. The experiments also indicate that the electronic resistivity of 10wt% MWNTs composite after heat treatment reduces approximately nine orders of magnitude over pure PBO polymer, but the tensile strength and modulus increase by 95% and 53%, respectively. MWNTs can obviously improve the thermal resistance of the composites.