Azide-terminated hyperbranched polyesters(HBPE-N₃) were prepared via the reaction between sodium azide and sulfonyloxy-terminated hyperbranched polyesters(HBPE-OTS) in dimethylsulfoxide(DMSO). The reaction conditions were optimized. Results show that up to 99.8% sulfonyloxy group can be substituted by azide groups when the temperature is 95 ℃, reaction time is 24 h, n(sodium azide):n(HBPE-OTS)=1.5 and the tetrabutylammonium bromide dosage is 5.0%(mole ratio)of sodium azide with DSMO as the reaction medium.