Hydroxyethylcellulose (HEC)-graft-poly(p-dioxanone) (PPDO) copolymer (HEC-g-PPDO) was synthesized homogeneously in ionic liquid 1-butyl-3-methylimidazolium chloride by coupling PPDO onto HEC backbone in the presence of 1,6-hexamethylene diisocyanate (HDI). When the feed ratio of PPDO and HEC was adjusted, as well as the molecular weight of PPDO, a series of HEC-g-PPDO copolymers with different microstructure parameters were obtained. The chemical structure, thermal stability, and thermal transition behaviors were investigated by FT-IR, H-1 NMR, TG, DSC, and nano DSC, respectively. These amphiphilic HEC-g-PPDO copolymers can self-assembly into micelles. The critical micelle concentration (CMC) and the hydrodynamic diameters were determined by fluorescence and dynamic light scattering (DLS) analyses. It was found that both the degree of substitution (DS) and polymerization (DP) of PPDO had an effect on the thermal stability, crystallization, and micellization of HEC-g-PPDO copolymers. Due to the crystallization of PPDO side chain, HEC-g-11.7PPDO0.15 whose DP and DS are 11.7 and 0.15, respectively, shows a minimum CMC value. The micelle size was in the range of 200-800 nm depending on the microstructure parameters of HEC-g-PPDO copolymers.