Natural Ca-Bentonite from Ebenebe in Anambra State, Nigeria, was successfully impregnated with Ca (NO3)2, Zn (NO3)2 and KOH and further calcined under different conditions of temperature and time using standard methods. Both the natural and impregnated bentonite clays were characterized using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Fluorescence Spectroscopy (XRF) and Scanning Electron Microscopy (SEM) and then applied as catalysts in transesterification reaction of refined castor oil. Viscosity reduction test was used to ascertain the best catalyst for the transesterification. FTIR spectra of the activated clay catalysts show the formation of new functional groups, as the intensity of the Al-O-H stretching group (3633cm-1) of the natural clay increased with slightly higher wavelengths of 3640cm-1, 3644cm-1, 3644cm-1, 3644cm-1, 3640cm-1and 3644cm-1 for CaB2, CaB3, ZnB2, ZnB3 KB400, and KB700 catalysts respectively. XRF result identified the natural bentonite clay as Ca-bentonite clay with Ca-oxide having the most dominant component of 76.71%. XRF chemical compositions of the six activated Ca-bentonite clay catalysts when compared to the natural Ca-bentonite clay confirmed successful impregnation. The SEM images of all the prepared catalysts showed that impregnation and calcination changed the surface morphology of the natural clay. Finally, transesterification reactions of refined castor oil samples were done with 3%w/w natural and impregnated Ca-bentonite catalysts, methanol to oil ratio of 6:1, 2 hours reaction time and 65oC reaction temperature. Results obtained showed a descending order of catalyst viscosity reduction ability to be KB700 > CaB3 > CaB2 > ZnB3 >NCB > ZnB2 > KB400.