Abstract: When we undertook the synthesis of Reichstein's substance S acetate and cortisone acetate from 17 α-hydroxy-progesterone and 17 α-hydroxy-ll-oxo-progesterone respectively by Joly's method, we introduced a modified procedure, in which chloroform and methyl alcohol were used as solvents in the synthesis of 21-iodo-intermediates, and the dimethylformamide as a solvent to convert 21-iodo-intermediate to 21-acetoxy steroids by reaction with anhydrous potassium acetate.After preliminary technical improvements, the yields of the synthesis of cortisone acetate and Reichstein's substance S acetate from 17 α-hydroxy-ll-oxo-progesterone and 17 α-hydroxy-progesterone respectively were raised to a new level of 80.181.1%, which is higher than Joly's method for about 10% and higher than Ringold's method for about 20%.