Gas-assisted injection molding process has been claimed by its proponents as the most important development for the injection molding process since the invention of reciprocating-screw injection molding machine. This process consists of a partial injection of polymer melt to the mold cavity followed by an injection of compressed gas which penetrates and, in principle, hollows out a network of pre-designed, thick-section gas channels until the cavity is filled. When the process is well developed and understood, it can produce many injection molded parts with light weight and high rigidity and will provide tremendous flexibility in the design of plastic parts. The analysis of the process involves flow of two drastically different materials in a geometrically complicated mold cavity. This study is aimed at establishing the scientific basis and attaining an engineering solution for characterizing this innovative process. Successful results of this research would not only expedite the development and acceptance of this process, but also may add a new dimension to the plastic part design.