The hydroxydation of the saturated fatty acids in order to prepare hydroxy fatty acids in the presence of catalysts was reported by several workers. The considering commercial applications of this reaction, authors studied on the hydroxydation of natural fats composed of nonhydroxy saturated fatty acids. Tallow and stearic acid were tested with manganese dioxide as catalyst, $110 {pm}3^{circ}C,$ and under atmospheric oxygen. The highest hydroxyl values were obtained at 20 hours for tallow, 107.6 and at 14 hours for stearic add, 116.0.