SummaryMethyl esters of castor oil were prepared by saponifying the oil with potassium hydroxide in methanol, splitting the potassium soapsin situ with an excess of hydrochloric acid, and esterifying at room temperature. The esters had hydroxyl values comparable with those of the parent oils. The methyl esters were quantitatively resolved into hydroxy and nonhydroxy esters after reacting with succinic anhydride in toluene. The composition of castor oil was calculated from a) amount of nonhydroxy esters, b) methyl linoleate content of methyl esters determined spectro‐photometrically, c) iodine value of the methyl esters determined by the Wijs method at 15–20°C., and d) iodine value of the nonhydroxy esters determined by the Woburn method. This composition was confirmed by the estimation of saturated acids in one sample and dihydroxystearic acid in all. Castor oil was readly hydrogenated with Raney nickel in alcohol at room temperature (30–33°C.) without any hydrogenolysis of the hydroxyl groups. Methyl dihydroxystearate content of the methyl esters of this hydrogenated oil was determined by reaction with 80–100% excess periodic acid at 15–20°C.