The updraft gasifier is a simple type of reactor for the gasification of biomass that is easy to operate and has high conversion efficiency, although it produces high levels of tar. This study attempts to observe the performance of a modified updraft gasifier. A modified updraft gasifier that recirculates the pyrolysis gases from drying zone back to the combustion zone and gas outlet at reduction zone was used. In this study, the level of pyrolysis gases that returned to the combustion zone was varied, and as well as measurements of gas composition, lower heating value and tar content. The results showed that an increase in the amount of pyrolysis gases that returned to the combustion zone resulted in a decrease in the amount of tar produced. An increase in the amount of recirculated gases tended to increase the concentrations of H2 and CH4 and reduce the concentration of CO with the primary (gasification) air flow held constant. Increasing the primary air flow tended to increase the amount of CO and decrease the amount of H2. The maximum of lower heating value was 4.9？MJ/m3. 1. Introduction The development of industry around the world has resulted in an enormous demand for energy that will continue to rise. However, the supply and the availability of energy from fossil fuels will decrease. Biomass is an environmentally sustainable alternative energy source that is widely available around the world [1]. Using biomass sources such as wood, rice husks, and bagasse, which have the highest energy content, together with the highest-efficiency conversion methods would add a significant amount of energy. The use of biomass for biofuels has reached approximately 9–14% of the total of energy demand worldwide [2]. Gasification is an ecoefficient and sustainable thermochemical conversion method [3] that creates low levels of pollution [4]. Various forms of gasifiers have been developed to meet criteria of being easy to operate, being highly efficient, and producing relatively low amounts of tar. The two most popular types of fixed-bed reactors used are the updraft gasifier and the downdraft gasifier. The updraft gasifier is easy to operate and has quite high conversion efficiency, but this type produces high levels of tar, as high as 0.2？kg/m3 [5], because the pyrolysis gases containing high levels of tar are extracted directly from the reactor. This increases the load on the gas cleaning system and the level of carcinogenic waste produced [1]. Modifying the reactor is one common method used to reduce the level of tar produced from the gasification. The gasifier
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