The chain conformations of poly(xylylene tetrahydrothiophenium chloride) (PXT) in the salt-free semidilute aqueous solutions, estimated from the double-logarithmic plots of reduced viscosity vs segmental concentrations, were found to be more extended when the molecular weight or chain length was decreased. The dissociation extent of counterions from the PXT chains estimated from the ionic conductivity measurements was also increased. Besides, when the molecular weight was over 150 000 g/mol, the chain, conformations were influenced more by the chain length than the counterion dissociation.