A new method was established for the determination of sodium dodecylbenzene suifnate（SDBS） in hogwash fat by ultraviolet-visible spectrophotometry.SDBS was extracted with distilled water,and reextracted with trichloromethane.The SDBS was determined after the coloration by methylene blue in the hogwash fat.The experimental factors such as extraction temperature and time were investigated.The optimal conditions were as follows:extraction time:2 h,extraction temperature:50 ℃ and detection wavelength:645 nm.Under the optimal conditions,the detection limit of SDBS was 0.1 μg/kg.The recoveries of SDBS in oil sample at spiked levels of 1.0,5.0,10.0,20.0 μg/kg were in the range of 94%-96% with RSDs less than 5%.The results of 5 groups of actual samples showed that the average of SDBS residues in hogwash fat was 19.19 μg/kg while the SDBS content in high-quality edible oil was 0.35 μg/kg.The testing results of actual samples showed that the SDBS contents in the hogwash fat were of big differences,but the contents were overall higher than those of the edible oil.The method could be used in the discrimination of hogwash fat.