The carbon nanotubes (CNTs) were reinforced with Poly(ethylene terephthalate) (PET) matrix resins to improve the electrical, thermal and mechanical properties of CNTs/PET composites in different contents of 0.25, 0.5, 0.75, 1.0, 1.25, 1.5 wt%. The powder material of PET and CNTs were first blended and then hot-pressed to form film specimen. The organizations and microstructures of the composites were studied with scanning electron microscope (SEM), the Atomic Force Microscope (AFM). The electrical resistivity of the composites was measured and was found to reduce rapidly when the contents of CNTs increase from 0 to 0.75%. The rate of reduction decreases as the contents of CNTs is greater than 0.75%. Temperature effect on the resistivity experiments indicates that the resistivity of the composites is not governed by CNTs, but the polymer materials between neighboring MWCNTs.