Cubic-framework sodium cobalt-based metaphosphate NaCo(PO3)(3) was recently demonstrated to be an attractive Nat cationic conductor. It can be potentially used in the next-generation rechargeable Na ion batteries. The crystal structure and electrical conductivity were studied and found to have a three-dimensional framework with interconnecting tunnels for Nat migration (J. Solid State Electrochem., 2016, 20, 1241). This inspired us to study the electrochemical (de)intercalation behavior of Nat in the NaCo(PO3)(3) assuming a cubic Pa3 framework. Herein, synergizing experimental and computational tools, we present the first report on the electrochemical activity and Nat diffusion pathway analysis of cubic NaCo(PO3)(3) prepared via conventional solid-state route. The electrochemical analyses reveal NaCo(PO3)(3) to be an active sodium insertion material with well-defined reversible Co3+/Co(2)t redox activity centered at 3.3 V (vs Na/Nat). Involving a solid-solution redox mechanism, close to 0.7 Nat per formula unit can be reversibly extracted. This experimental finding is augmented with bond valence site energy (BVSE) modeling to clarify Nat migration in cubic NaCo(PO3)(3). BVSE analyses suggest feasible Nat migration with moderate energy barrier of 0.68 eV. Cubic NaCo(PO3)(3) forms a 3.3 V sodium insertion material.