SummaryThe surface chemical composition and microstructure of walnut protein obtained through aqueous buffer and bis(2‐ethylhexyl) sodium sulfosuccinate (AOT) reverse micelles were determined by X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The surfaces were characterised by XPS to monitor surface composition. The different components of C 1s, N 1s and O 1s peaks were provided precisely. By comparison with walnut protein surface from aqueous buffer, XPS analysis revealed that the O atomic percentage of walnut protein powder surface from AOT reverse micelles was higher, but the C and N atomic percentages were lower. The N/C ratio of the walnut protein powders using two extraction methods was similar, while significant difference was obtained in the O/N. The obtained results indicated that the reverse micelles could affect the C, O and N components on the surface of walnut protein powder. Protein microstructure after reverse micelle treatment showed many crystals.