Crude extract of rapeseed cake was fractionated and alkaline-hydrolyzed to convert sinapine into sinapic acid, and the produced hydrolyzed extract showed higher antimicrobial and antioxidative activities than the crude extract. When the hydrolyzed extract was added to mayonnaise dressing, microbial stability increased along with physical characteristics and oxidative stability, thereby supporting the potential of hydrolyzed rapeseed extract as a food additive for quality management of mayonnaise dressing during storage.