Failure in transformers could be caused by the corrosive sulfur in their oil. Preliminary studies on the test of corrosive sulfur in transformer oil and temperature are performed. The comparison among their results of their typical test methods for corrosive sulfur is discussed. It is illustrated that the corrosive-sulfur sensitivity is varied with the test conditions. Temperature is the important factor for the reaction of corrosive sulfur with copper. We have done experiments of specimen immersing and mercaptan content in oil, so we can confirm that high temperature enhances the reaction.