Hydrodynamic methods and light scattering were used in the studies of solutions of a surface active monomer 11-acryloyloxyundecyltrimethylammonium bromide (AUTA-Br) and its polymers in 0.05 M NaCl. Aqueous solutions of AUTA-Br monomer in the concentration range of 4 to 16 CMC contain individual molecules and near-spherical AUTA-Br aggregates. The pAUTA-Br polymers possess rather high equilibrium rigidity (11.8 nm). This high value of equilibrium rigidity found for pAUTA-Br macromolecules is apparently caused by two factors: the presence of a bulky side substituent in each AUTA-Br monomer unit and incomplete suppression of electrostatic interactions between neighboring monomer units in the backbone.