There is a great interest in developing efficient electrode materials for sodium-ion batteries, which are currently being projected as a promising alternative to lithium-ion batteries. Here we report the synthesis of a sodium-ion battery cathode material, Na0.5Ni0.25Mn0.75O2, through a sol-gel method. The as-synthesized layered Na0.5Ni0.25Mn0.75O2 material exhibits a layered P2-type structure, and shows excellent electrochemical properties when studied as a cathode for sodium-ion batteries, with a specific discharge capacity of 210mAhg−1 and a good capacity retention of 80% at 50th cycle in the voltage range from 1.5 to 4.4V at 0.1C. The layered Na0.5Ni0.25Mn0.75O2 material also exhibits good cycling stability with remarkably smooth and flat charge-discharge profiles at a high voltage of 4.1V vs Na. The overall electrochemical performance of layered Na0.5Ni0.25Mn0.75O2 is quite promising, and hence the present study will greatly contribute to the on-going search for advanced and efficient electrodes for sodium-ion batteries.