Stable O and H isotope compositions were measured of pure mineral separates of weathering minerals (gibbsite and kaolinite) from lateritic residuum developed over Deccan basalt in the Kolhapur district, Maharastra. The δ18O (‰, VSMOW) versus δD (‰, VSMOW) values of gibbsite samples range from 2.50 to 7.41 and -50 to -53, respectively, and those for kaolinite samples range from 16.4 to 17.8 and -73 to -77, respectively. Plots of isotope data of gibbsite on a bivariate δ18O versus δD diagram indicate that the analyzed gibbsites are of secondary origin. The calculated values of δ18Owater in equilibrium with gibbsite suggest their formation under intense monsoonal conditions, significantly different from the present day climate of the study area