Abstract: Life cycle assessment was applied to evaluate the environmental impact of the post-tanning process of four retanning agents including aromatic syntan BTL, melamine resin DD42, acrylic resin LP and mimosa extract SUN. Results indicate that the retanning agent and the corresponding retanning operation are the important contributors to the environmental impact of post-tanning process, and the environmental impact sequence of the four tested retanning agents is BTL>DD42>LP>SUN. The abiotic depletion potential, primary energy demand, and climate warming potential of the SUN post-tanning process were reduced by 61%, 39%, and 46%, respectively, compared with that of LP post-tanning process, and were decreased by 73%, 55%, and 59%, respectively, compared with that of BTL post-tanning process. This is because only a few mineral and petrochemical resources were consumed and a little greenhouse gas was discharged in the SUN production process. Compared with the LP and SUN post-tanning processes, BTL and DD42 post-tanning processes exhibited remarkably higher environmental impact on the ecological quality and human health, because formaldehyde was used in the production processes of both BTL and DD42. Thus, formaldehyde-free biomass-based materials, i.e. vegetable extracts, are green retanning agents for leather post-tanning systems.