Polypropylene/biomass waste composites and their constituents were gasified with steam by a two-stage process, in a dual-bed microreactor for the production of fuel gases. Gasification experiments were carried out at 700 °C gasification temperature in absence and presence of Fe2O3/CeO2 catalyst. The gases produced during the process were mainly H2, CO, CO2, CH4, and some light hydrocarbons. The use of Fe2O3/CeO2 catalyst in the steam gasification of plastic, biomasses, and plastic/biomass composites resulted in the increase in production of gaseous products, indicating that the catalyst accelerated the gasification rate. Moreover, a synergistic effect of combining plastics with biomass was observed since the amount of H2 production increased in the case of PP/biomass composites compared to the added contribution of production of H2 from the individual components.