The method for obtaining an acid solution containing nickel is obtained by treating a positive electrode material of a nickel-metal hydride battery. The method includes a water-washing step, wherein a positive electrode material of a nickel-metal hydride battery is water-washed by adding water, and then separated to form a positive electrode material after water-washing and a water-washed slurry. An acid-washing step then is performed, wherein an acid is added and mixed into the positive electrode material obtained after water-washing in the water-washing step, and, separation is performed to form a positive electrode material after acid-washing and an acid-washed slurry. A dissolution step is performed wherein the positive electrode material obtained in the acid-washing step is separated into a nickel solution and a dissolution residue by adding any one of an acid and an oxidizing agent.