Abstract: Alkyl ketene Dimer(AKD)and Alkenyl succinic Anhydride(ASA)are easily hydrolyzed in water, and the anionic trash was formed by their hydrolysis product. Beyond that, AKD has the problem of sizing hysteresis and ASA need to be emulsified on the spot. Stearylamidoethyl epoxypropyl ammonium chloride(SEAC)is a stable cationic sizing agent without sizing hysteresis. Firstly, diethylenetriamine can form fattymide through amidation reaction with stearic acid. The secondary amine can further form quaternary ammonium after ring open reaction of epichlorohydrin. This paper mainly discussed the material ratio and the reaction kinetics parameters. The molecular structures and composition were identified and examined by IR and C¹¹³ NMR. Experimental results showed the melting point of stearamide was lower than 105 ℃ when diethylenetriamine/ stearic acid ratio was 1.5:1 at 160 ℃for 3.5 h reaction time. SEAC whose melting point was about 70 ℃ had good sizing when cationic temperature was at 70 ℃ for 2.5 h. Experimental results demonstrated that SEAC overcamed the disadvantages of AKD and was one kind of great potential sizing agent.