AbstractThe intrinsic viscosities and sedimentation constants of polymethacrylic acid‐poly‐vinylpyrrolidone (PMAA‐PVP) mixtures have been measured in water and dimethylsulf‐oxide. By conductometric method it has been shown that the composition of those complexes is stoichiometric.The value of intrinsic viscosity of the complexes in water is about 0.10 dl/g which is close to the viscosity of globular proteins. This value seems to be almost independent of the concentration and molecular weight of the macromolecular components of the complex (both PMAA and PVP have been used as an oligomer and as an matrix), and in the case of high molecular weight of both the components as well.In an organic solvent a sharp increase of intrinsic viscosity is observed. This is probably connected with the weakening of hydrophobic bonds stabilizing the compact structure of complex in water. In dimethylsulfoxide reduced viscosity depends on concentration and intrinsic viscosity on the molecular weight of the matrix (PMAA). The values of hydrodynamic‐average molecular weights of complexes establish the intermolecular association of complexes particles in water, and the degree of association depending on the molecular weight of the matrix. In dimethylsulfoxide probably not only the weakening of hydrophobic interactions but the destruction of hydrogen bonds occurs, following which the dissolution of the complexestakes places. In water‐dimethylsulfoxide mixtures a gradual destruction of the complex is observed at the transition from water to orga