The conductance and counterion activity of aliphatic ionenes with counterions of F-, Cl-, Br-, I-, and NO3- in both the absence and presence of salts were measured and compared with Manning＇s equations for both cases. Samples used were 3,3-, 4,5-, 6,6-, and 6,9-ionenes, where the numbers are those of methylene groups between the quaternized nitrogen atoms. The activity coefficients of counterions for ionenes in the absence of salts were lower than the theoretical values, and experimentally determined values of the charge density parameters, higher than the theoretical ones, could explain the departure between the experimental and the theoretical values at least semiquantitatively. The conductance of ionenes in the presence of salts deviated from the additivity rules, dependent on charge density of the ionenes as well as the counterions used. It also deviated from the theoretical prediction in which the interaction between small ions was taken into account. On the other hand, the additivity holds approximately for the counterion activity irrespective of the species of ionenes and counterions, in marked contrast to the case of conductivity. The viscosity of the ionene solution exhibited a strong dependence on the salts added. The effect of salts on the viscosity was more prominent in the samples with higher charge density parameter, corresponding to larger conformational change in the polyion. These results may give useful information on the conformation of ionenes in solution as well as the mechanism of the electrical conductivity of polyelectrolytes.