Foam injection molding is a process by which complex, thick parts with a cellular core and a compact solid skin can be manufactured. The addition of a physical blowing agent under high pressure allows the decrease of the viscosity and the glass transition temperature of the gas/polymer melt. These features of the foam injection molding are very beneficial for biodegradable polymers, in which the processability window is very narrow. In this study, morphology, rheological, and mechanical properties of parts with a complex shape, obtained by foam injection molding, were analyzed. In particular, two commercial grades of poly(lactic acid) having different rheological behavior were adopted to obtain foamed parts by injection molding process with nitrogen as a physical blowing agent. For both resins, the effect of the mold opening on morphology and mechanical properties was assessed. POLYM. ENG. SCI., 58:475-484, 2018. (c) 2017 Society of Plastics Engineers