Abstract: The effects of the loop density for rib 1∶1 fabric preform made from GF/PP commingled yarn on the tensile properties of composites were investigated. Six samples of rib 1∶1 fabric preform with different loop densities were studied. It was found that the tensile strength of composites showed an increase followed by a slightly decrease as the increase of the loop density of the rib 1∶1 fabric preform, while the fracture strain just varied contrarily. This phenomenon was explained from the inherent characteristic of loop structure, the homogeneity of fiber/matrix distribution in composites and the continuousness of the reinforced fiber. Micrographic studies using optical and scanning electron microscopy revealed that the void content in the composite decreased as the loop density of the preform increased and the fiber and matrix distributed more uniformly, meanwhile, more glass fiber was broken because of the reduction of the radius of curvature of the loop.