This study was conducted to find out the co-operative effect of antioxidants (butyl hydroxy anisol, dibutyl hydroxy toluene, propyl gallate) and pyrophosphate (tetrasodium pyrophosphate, disodium pyrophosphate) on the stability of soybean oil by determining the peroxide values. The results obtained were summarized follows: 1. When antioxidants and pyrophosphates were used together, the antioxidants activity was more strong than antioxidants were used only. 2. The co-operative effect of disodium pyrophosphate for antioxidants was stronger than tetrasodium pyrophosphate.