Sawdust is a waste that can be used as a source of renewable energy, using gasification technology. Biomass gasification technology is a simple and easy technology in its operation and deserves to be continuously improved technically and economically. Thus biomass gasification technology has the potential to be the right technology to be applied throughout Indonesia. The gasification process is carried out by flowing the reaction between air and biomass in dry sawdust to produce the combustible gas. Biomass in the form of sengon wood sawdust should be dried to test with an updraft type gasification stove with a fuel capacity of 1300 grams. The test uses two variations, namely variations in air velocity and variations in the charcoal mixture. The variation of the air velocity itself is divided into three air velocity (V) of 0.7 m / s, 0.9 m / s, and 1.05 m / s. While the variation of the biomass mixture is divided into four charcoal mixtures, namely 0% (without charcoal mixture), 25%, 50%, 75%, and 100% (without sawdust). The results of this study get the value of thermal efficiency on variations in air velocity. The highest efficiency value is at V = 1.05 m / s with an efficiency value of 27.49%, V = 0.9 m / s of 17.42%, and V = 0.7 m / s of 14.49% . Whereas in the variation of charcoal thickness, the highest thermal efficiency value was obtained in a mixture of 25% charcoal by 35.04%, in a mixture of 50% charcoal by 32.38%, in a mixture of 75% charcoal by 21.64%, and in a mixture of 100% charcoal 17.11%.