Abstract: Sodium maleopimaric acid octadecamide dicarboxylate(C₁₈MPA2Na) was synthesized from rosin by D-A addition, amidation and acid-base neutralization reactions. The structure was characterized by FT-IR, ¹H NMR and mass spectrometry. Surface tension method and Nile red(NR) fluorescence probe method were used to study the surface activity of C₁₈MPA2Na. The critical micelle concentration(cmc) of C₁₈MPa2Na was 0.29 mmol/L, the surface tension value at cmc(γ_cmc) was 41.11 mN/m, and it showed good surface activity. A viscoelastic solutions were successfully prepared by combining C₁₈MPA2Na with cetyltrimethyl ammonium bromide(CTAB). The microstructure and rheological behavior of the composite system were studied by in situ cryo-electron microscopy(Cryo-TEM) and rheology. The results showed that the aggregates of the C₁₈MPA2Na/CTAB viscoelastic solutions were wormlike micelles. When the CTAB concentration in the complex system was fixed at 80 mmol/L, the zero-shear viscosity(η₀) first increased and then decreased with the increase of C₁₈MPA2Na concentration. The maximum value of η₀ was 5.67×10⁴ mPa·s at the C₁₈MPA2Na concentration of 15 mmol/L. When the ratio of C₁₈ MPA2Na to CTAB(3 ∶ 16) was fixed, η₀ showed a trend of rapid increase and then tended to be constant with the increase of C₁₈MPA2Na and CTAB concentrations in the mixed system. The power index value of η₀ to concentration was 11.7. At C₁₈MPA2Na concentration of 15 mmol/L and CTAB concentration of 80 mmol/L, with the decrease of pH values, η₀ increased first and then decreased, and reached the maximum value(7.67×10⁴mPa · s) at the pH of 7.13. This study demonstrated that the rigid skeleton of rosin could promote the self-assembly of surfactants.