In this work, we consider the tensiometric behavior of the system poly(N-octyl-4-vinylpyridinium bromide)(20%)/sodium dodecylsulfate [ P4VPC8-20-SDS ] in absence and the presence of NaCl salt. Thus, t he copolymer poly(N-octyl-4-vinylpyridinium bromide)(2 0%) [ P4VPC8-20 ] is used under quaternization rate of 20%. The results show that the copolymer concentration p lays a main role in the tensiometric behavior of th is system. Also, the salt addition decreases the surface tensi on of the solution. Finally, the surface tension of the solution decreases as a function of the SDS concentrations f or all the copolymer concentrations. All the result s confirm the main role of the electrostatic interactions and the importance of the copolymer character in term of t he hydrophobic/hydrophylic balance.