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. © 2016 Institution of Engineering and Technology. All rights reserved.