Objective To study the process of removing bacterial endotoxins by ultrafiltration technology in dextran 40 injection. Methods Dextran 40 solution was ultrafiltrated by 100,200,and 300 kDa aperture ultrafiltration membranes with composite, PES and PVDF materials. In order to optimize ultrafiltration process,the content of effective component and endotoxins were detected by HPLC and kinetic-turbidimetry,respectively,and the change of particle size distribution in dextran 40 solution was analyzed before and after ultrafiltration. Results The transmittance of dextran 40 was close to the same MWCO and different membrane material. When MWCO reached 300 kDa,the transmittance was above 91%,which met the requirement of filtration. The endotoxin removal rates by 100-300 kDa composite ultrafiltration membranes were more than 99%. But the endotoxin removal rates of both of PES and PVDF membranes were less than 40%,which were unable to guarantee the removal efficiency of the endotoxin in dextran 40 solution. The particle size declined after ultrafiltration by 300 kDa composite membrane, and level of the insoluble particles decreased. Conclusion The 300 kDa composite ultrafiltration membrane can effectively remove endotoxin in dextran 40 solution with less main components loss. The material can meet requirements for producing dextran 40 injection.