Abstract: A water-soluble carboxyl terminated hyperbranched polyester HBP-4 (M_w = 1909, DB (degree of branching) = 0.72) was used as high absorption chrome tanning auxiliary. Firstly, the effect of HBP-4 on the alkali resistance of chrome tanning agent was determined. Then the optimum application process of HBP-4 was investigated by changing its dosage and adding time. The results showed that when the HBP-4 was added at the beginning of basifying treatment and the dosage of HBP-4 was 1.5% of the leather weight, the chromium absorption rate was increased by 22.3%, the shrinkage temperature of wet-blue leather was increased by 5 ℃, and the tensile strength of leather was increased by 86.2%. The SEM photos for the fracture surface of tanned wet-blue leather confirmed that HBP-4 could increase the crosslinking density of collagen fibers. Moreover, HBP-4 can also improve the chrome absorption, thermal stability and mechanical property of leather in the self-alkalifying chrome tanning.