Disrupted supply of biomass due to seasonal harvesting, climate change, and transportation cost are challenge for continuous biomass gasification operation. Co-gasification is a potential solution for this problem; however, little information is available about co-gasification of different biomass materials. In this study, two tropical plant-based biomass, oil palm fronds (OPF) and coconut shells (CS) were co-gasified in fixed-bed downdraft gasifier at constant airflow rate. The blends of OPF/CS at the ratios of 80:20, 60:40, 40:60, and 20:80 were considered for co-gasification experiments and gasification of pure OPF and CS were carried out at the maximum material size of 10-25 mm. The effect of biomass blending ratio on syngas quality and performance of co-gasification were investigated. The results show that CO, H₂, and syngas higher heating value increased by up to 18%, 16%, and 14%, respectively, as compared to gasification of single biomass. The carbon conversion efficiency and cold gas efficiency were also observed to be higher than 95% and 60%, respectively. In many cogasification cases, quality of syngas and performance of cogasification were better than using 100% gasification of OPF and CS, which is most important finding of this work. Therefore, co-gasification of the blended feedstock has a significant potential to overcoming the problem of disrupted feedstock supply in gasification.