In this paper, the ionic conductivity of a new polymer solid electrolyte prepared by employing both intermacromolecular complexation and plasticization was studied. The experimental results show that a decrease in the molecular weight of the plasticizer, or an increase in the plasticizer content, led to an increase in the ionic conductivity σ of the system. The equal mole ratio of P(MMA-MAA) to PEO and a higher concentration of lithium salt favour an increase in σ. In addition, σ increases with increased temperature and frequency. The system containing the alkali metal salt of a smaller cation or larger anion exhibits higher ionic conductivity.