Gasification is a technique in which biomass is converted into low/medium heating value producer gas which is rich in H 2 and CO. The present work deals with the thermodynamic and heat transfer analysis of the downdraft gasification system with different feedstock.These analyses are very important to understand the utilization of the feedstock in the gasifier reactor. In this work, mass balance, element balance, energy balance, and heat transfer analysis were carried out for the gasification process. For the analysis purpose, five different feedstock such as lignite, cumin briquette + sawdust briquette (40:60, w/ w), sawdust briquette, wood, and lignite + wood (50:50, w/w) were used in 10 kWe atmospheric pressure downdraft gasifier system. Mass Balance Closure (MBC), Energy Balance Closure (ENBC), and Element Balance Closure (EBC) were found in the range of 0.95-1.03, 0.93-0.97 and 0.84-1.09, respectively. The infrared thermal imager was used to measure the surface temperature of the gasifier reactor which results were used to calculate convective and radiative heat lossesfrom the gasifier reactor.The convective and radiative heat losses were found in the range of 0.511 kW to 0.802 kW and 0.255 kW to 0.431 kW, respectively for the selected feedstock.