The sizes (hydrodynamic diameter) and ζ potentials of sodium N-acryloyl-11-aminoundecanoate and poly(sodium N-acryloyl-11-aminoundecanoate) with molecular weights of 10 000, 100 000, and 250 000 were determined using dynamic light scattering. The particle size of the formed aggregates of the macromolecules depends on the molecular weight. The value of ζ potential of the aggregates increases with an increase in the molecular weight of the polymer. The influence of the systems based on the monomer and polymers on the alkaline hydrolysis of 4-nitrophenyl chloroethyl methylphosphonate was studied by spectrophotometry. The character and extent of effect of the system depend on the molecular weight of the polymer and type of the counterion. The strongest inhibition of the process (by 65 times) is observed in the case of poly(sodium N-acryloyl-11-aminoundecanoate) with the molecular weight 100 000.