Abstract: In this paper, first of all, the conductivity of sodium polymethacrylate of different molecular weight has been investigated at different temperatures. Secondly, the conductivity of lithium, sodium and potassium polymethacrylate has been determined at different temperatures, and the effects of ionic radius on conductivity have been compared. Finally, the effects of side chain length of polyelectrolytes on the conductivity have been studied.Conductivity has been determined by means of direct current method. The complex relations between conductivity of polyelectrolyte and molecular weight are showed. Conductivity depends on the number of ion, which disassociate from the chain, and molecular weight. The results of experiment indicate that the relation between conductivity and ionic radius change as the shape of V. Among salts of lithium, sodium and potassium, the sodium is in the lowest. Linear lgo vs. 1/Tplots are obtained for polyelectrolytes.