ABSTRACT: Polymeric nanospheres with uniform sizes, functional surfaces, and high mechanical strength and thermostability are attracting wide interest in different applications. Here, a new kind of polysulfone micellar spheres with PEGylated surfaces is prepared via directly heating the solution of an amphiphilic block copolymer, polysulfone‐b‐polyethylene glycol (PSF‐b‐PEG). The sizes of the micelles are uniform and tunable between ∼42 and ∼443 nm. TEM characterizations show that the micelles are core‐shell structures with PEG as the corona and PSF as the core. PEG endows the micelles with dispersibility in water and good biocompatibility, while PSF provides the mechanical strength and thermostability. The effects of PEG contents, polymer solution concentrations, solvent types, and heating temperatures are systematically investigated. Furthermore, heat resistance tests show that the micelles are stable at 150–180 °C. These PSF‐b‐PEG micellar spheres are expected to be applied in demanding environmental conditions such as heating involved surface modification process. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 769–777 [ABSTRACT FROM AUTHOR]