Parametric study of co-gasification of rice straw (RS), high-density polyethylene (PE) and Polyvinylchloride (PVC) was carried out to investigate the effect of temperature, flow rate of steam, typical plastics and their blends on the quality and volume of synthetic gas. The additions of plastic enhance H2 content in the synthetic gas. The study found that increase in temperature increases the yield of synthetic gas, H2 and CO content and lower heating value (LHV) of synthetic gas. The steam to biomass ratio seems to have a very small effect on gas composition. Likewise the increase in PE content in the feed blend increases the hydrogen content and gas yield. Similar results were obtained by increasing PVC content. Co-gasification experiments of ternary blends of RS, PE and PVC were also conducted. The ternary blends of 20 % RS, 40 % PE, 40 % PVC produced synthetic gas with higher H2 content, higher synthetic gas production rate and higher LHV of synthetic gas. This work confirms that synergistic interactive effect takes place during the co-gasification of ternary blends of PE, PVC and RS due to volatile-char interaction and mineral catalytic effects. This work also suggests that carefully designed co-gasification unit can handle waste with varying composition of biomass and plastic to produce improved quantity as well as quality of synthetic gas.