Abstract: Comprehensive systemic investigation of seventy oil-extracting factories was made. It was found that the contents of gossypol in the crude oil produced by the method of extraction of natural or heated cotton seeds were higher than the national standard for edible vegetable oil,but could be lowered to meet the standard after alkaline refining. No heavy metals was detected in the oil produced by both methods. The alkaline refined oil which was extracted by these two methods showed so significant difference with respect to the yield of oil and adverse influence on persons who used it in food.