This study deals with the covalorization of spent bleaching clay (SBC) and palm fatty acid distillate (PFAD), the by-products of palm oil-refining plants (3 Mt. year-1), through soap manufacture. Obtained SBC and PFAD samples show differing acidity and saponification values depending on their content of free fatty acids and of acylglycerols. The SBC sample had an acidity of 60.5% and a saponification value of 182 mg KOH g-1 of oil, and the PFAD sample has an acidity of 88.4% and a saponification value of 204 mg KOH g-1 of oil. Soaps are prepared using the stoichiometric amount of NaOH, under varying proportion of water introduced through the basic solution. The overall reaction (neutralization and saponification) is complete (99.9%) with PFAD, whereas the yield reaches only 56.1% with SBC. When mixing SBC and PFAD, for example under a 1:1 weight ratio, the overall reaction completion (87.7%) is surprisingly higher than expected based on the computed individual reaction yields (78%), showing a synergistic effect of about 10% on the course of the saponification reaction of acylglycerols in SBC. The water content was found to be a critical parameter, 30% w/w of added water providing the highest yield. These results show an innovative way for covalorizing two important by-products of palm oil industrial processing as a single final product. By-products of the physical refining of other oils could also be valorized following the same method.