The present work studies gasification of high ash biomass (20-25% w/w), high ash coal (30-35% w/w), and their co-gasification in a downdraft gasifier developed in our earlier study (Siddiqui a al., 2018). TGA studies were performed to examine the change in performance due to the catalytic effect of inorganic content. The effect of biomass ratio (BR) was examined. Higher percentage of biomass increased the conversion to gas on carbon basis, and decreased the conversions to char and tar. The presence of coal enhanced the temperature and hence the rates of the reactions to certain extent. The respective cold gas and thermal efficiencies for BR0 are 33.06% and 49.38%, and for BR1 are 52.22% and 64.15%. BRO.75 gave the best performance with CGE of 57.5% and thermal efficiency of 72.63%. Finally, the clinker formation issue and the preliminary atmospheric emissions measurements are reported for gasifier.