Display omitted •Preparation of chitosan sulfate by using an industrial recognized green and highly reactive sulfating agent gas SO3.•The synthesized chitosan sulfate had a high sulfur content.•Vesicles formed in the aqueous mixture of chitosan sulfate and cetyltrimethylammonium bromide. Chitosan of high molecular weight and 85% deacetylation was used to prepare chitosan sulfate (CHS) by employing an industrial recognized green and highly reactive sulfating agent gas SO3. FT-IR and solid-state CP-MAS 13C NMR spectra confirmed that sulfate groups were successfully introduced into chitosan chains with a sulfur content of 16.50% and the substitution degree of 1.75 according to the results of elemental analysis. The aggregation behavior of the mixture of chitosan sulfate polyelectrolyte and oppositely charged surfactant cetyltrimethylammonium bromide (CTAB) was characterized by surface tension, steady-state fluorescent, turbidity, ζ potential and transmission electron microscopy. The results indicate that the CHS/CTAB mixture has pretty high surface activity and low critical aggregation concentration. The CHS/CTAB mixture successively forms spherical aggregates, precipitation, vesicles and micelle aggregates coated by CHS chains by increasing surfactant concentration due to the cooperative hydrophobic and electrostatic interactions.