A solution for removing an aluminum oxide film from an aluminum or aluminum alloy surface, which includes a salt or oxide of a metal capable of substituting aluminum, a solubilizing agent for ions of the metal, and an alkali, and which has a pH Of 10 to 13.5.The removing solution makes it possible to form a film of the metal derived from the metal salt or oxide contained in the removing solution by dissolving away the oxide film from the aluminum or aluminum alloy surface at a low temperature and a high speed while restraining, as securely as possible, erosion of the aluminum or aluminum alloy surface. Besides, the removing solution ensures that even in the case where the thickness of the aluminum or aluminum alloy basis material is very small, the aluminum or aluminum alloy surface can be activated while assuredly leaving the aluminum or aluminum alloy basis material.