A single phase O3-type layered NaNi0.5Mn0.3Ti0.2O2 compound synthesized via simple solid-state reaction is first reported as a promising cathode material for sodium-ion batteries. A high reversible capacity of approximately 138 mAh g−1 and initial coulombic efficiency of above 96% can be obtained in half-cell. The performance of sodium-ion full-cells with NaNi0.5Mn0.3Ti0.2O2 as the cathode and presodiated hard carbon as the anodes were also evaluated. Based on the mass of cathode, the full-cells can still exhibit a high reversible capacity of ca. 131 mAh g−1. The prominent capacities make NaNi0.5Mn0.3Ti0.2O2 as an important cathode candidate for room temperature sodium-ion batteries.