A cost effective and efficient method for the preparation of fuel grade biodiesel by the transesterification of jatropha oil at room temperature over a coconut husk derived catalyst under mild reaction conditions without the use of any cosolvent is reported here. Catalyst is prepared by means of controlled heating of coconut husk, without any chemical treatment. The main active component over the catalyst was found to be potassium. When the reaction temperature was increased to 45 degrees C, the catalyst showed excellent performance on the transesterification of Jatropha oil in a range of methanol/oil molar ratios. The important speciality for the present catalytic systems is the comparatively low reaction temperature requirement for effective reaction. For the optimization of different reaction variables including molar ratio of the reactants, reaction time, the catalyst calcination temperatures and the catalyst/oil weight percentage, a series of transesterification reactions were conducted and the results obtained are presented here. (C) 2014 Elsevier Ltd. All rights reserved.