Abstract: A new leather-making fatliquoring agent MADO-SUL was prepared using maleic anhydride (MAH) as starting material. It was reacted in order with diethylene glycol diethyl ether, stearyl alcohol and sodium sulfite respectively, which involved two-step esterification and a sulfonation reaction. A series of single factor experiments were carried out to explore the optimum synthesis conditions. It was found that the optimum synthesis temperature of MADG, the product of first esterification, was 90 ℃ and the reaction time was 5 h with the molar ratio of maleic anhydride to diethylene glycol diethyl ether to be 1∶1. Additionally, the product of second esterification reaction was named MADO and the optimum reaction temperature was 190 ℃, the reaction time was 7 h and the molar ratio of MADG to stearyl alcohol was 1∶1. Furthermore, phosphorous acid was selected as catalyst and its dosage was 0.5% of total reaction system on weight basis. As for sulfonation reaction, its optimum temperature was 80 ℃, the optimum time was 5 h, and the molar ratio of MADO to sodium sulfite was 1∶1. The structure of MADO-SUL was analyzed by FT-IR and ¹H-NMR. Moreover, MADO-SUL was applied to fatliquoring experiment of cowhide blue wet leather and compared with commercial fatliquoring agent SF. It was found that the prepared MADO-SUL exhibited promising performances, and the dichloromethane extracted content of leather fatliquored by MADO-SUL was 3.224% and the content of volatile organic compounds (VOCs) was 92.484 μgC/g, both lower than that of leather fatliquored by commercial fatliquoring agent, which were 5.4855% and 173.348 μgC/g, respectively.