An aqueous zinc nitrite solution which contains substantially no calcium (Ca) ions is provided, in which, in terms of the aqueous zinc nitrite [Zn(NO.sub.2).sub.2] solution having an NO.sub.2 concentration of 10% by weight, the sodium (Na) ion concentration is 200 to 2000 ppm and the sulfate (SO.sub.4) ion concentration is 20 ppm or less in the solution. The aqueous zinc nitrite solution can be prepared by providing a zinc compound and an alkali nitrite as raw materials and subjecting the raw materials to electrolytic synthesis through a double decomposition reaction using an ion-exchange membrane as a diaphragm. As the aqueous zinc nitrite solution is provided, an extremely efficient metal surface treatment is made possible which has a reduced amount of sodium ions. In particular, it contains substantially no sulfate ions and no calcium ions.