Glass fiber reinforced plastics (GFRP) have higher mechanical strength and lower heat deflection comparing virgin plastic materials. However, GFRP has disadvantages such as heavy weight and warping, and to solve these problems foaming process has applied. In this study, two ways of foaming process for injection molding has performed ?chemical foaming and physical foaming. Polypropylene and glass fiber reinforced polypropylene have chosen as materials. Foaming characteristics, foaming ratio and cell morphology, is measured and mechanical properties are observed. As a result, the effect of glass fiber on foaming process has derived.