Bio-energy is now considered as having the potential to provide the major part of the projected renewable energy provisions of the future. Slow pyrolysis is one of the three main thermal routes, with gasification and combustion, for providing a useful and valuable bio-fuel. Slow thermal pyrolysis of castor seeds were carried out in a semi batch reactor made up of stainless steel at temperature range from 450 degrees C to 600 degrees C to produce bio-fuel. This paper studied the effect of temperature on pyrolysis of castor seeds to find the optimum temperature of maximum liquid yield. The thermal degradation temperature of castor seed was studied using thermo gravimetric analysis (TGA) at a heating rate of 20 degrees C/min in air atmosphere. The oil samples obtained at optimum condition is analyzed according to their fuel properties, elemental analysis, functional group presents, and compounds presents. (c) 2011 Elsevier Ltd. All rights reserved.