An active basic solid catalyst for biodiesel production was obtained via KOH impregnation onto sepiolite support followed by high temperature calcination. The transesterification of rapeseed oil over the resulting nanocomposite structure was investigated using a microwave reactor. Morphological and structural characterization of sepiolite and KOH impregnated sepiolite was carried out by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy analysis. Optimization of the operational parameters such as methanol to oil molar ratio, catalyst loading, reaction temperature and reaction time were examined. Reusability of the catalyst and the reactions utilizing waste cooking oil were also studied. Obtained results indicated that the basic heterogeneous catalysis diminishes the saponification during the transesterification reaction and that microwave heating was very effective at shortening the biodiesel production time. However, the reusability of the KOH impregnated sepiolite catalysts and their structural stability require further investigation