The effect of plasticizer addition on the density, conductivity, glass transition, and free volume behavior of salt containing polyether-urethanes has been examined. The addition of up to 1.5 molal LiC1O4 salt results in an effective crosslinking of the polyether-urethane chains due to the Li+ coordination with the oxygens of the host polymer. This crosslinking decreases inter- and intrachain separation and reduces polymer chain mobility as illustrated by increased density and Tg, decreased free volume, and, at salt concentrations greater than 0.6 molal, decreased conductivity. The addition of approximately 30 wt % tetraglyme plasticizer to the 1 molal LiC1O4/host polymer complex is shown to counter the effective crosslinking resulting in a decreased Tg to a value equal to that of the pure host polymer, increased conductivity, and increased average free volume cavity size to a value equal to that of the pure host polymer. However, the relative number of free volume cavities in the plasticized host polymer/salt complex remains fewer than that of the pure host polymer over the concentration range of plasticizer studied, and in a similar manner the density remains greater than that of the pure host polymer. The room temperature conductivity, free volume, and density behavior in conjunction with the Tg results suggest that the plasticizer addition leads to Li+ coordination with the oxygens of the plasticizer chains as well as increased mobility of the host polymer chains.