A method is disclosed for increasing the rate of vulcanization of a sulfur rubber composition comprising heating a sulfur vulcanizable rubber composition to a temperature ranging from 100.degree. C. to 200.degree. C., said rubber composition, containing a sulfur vulcanizable rubber, a sulfenamide compound and a hydrated thiosulfate. Addition of the hydrated thiosulfate to a sulfur vulcanizable rubber and a sulfenamide compound significantly increases the rate of vulcanization of the rubber.