The present invention provides a chemical solution having excellent storage stability and excellent defect inhibition performance. The present invention also provides a method for treating a substrate. The chemical solution according to an embodiment of the present invention is a chemical solution used for removing a transition metal-containing substance on a substrate. The chemical solution contains one or more kinds of halogen oxoacids selected from the group consisting of a halogen oxoacid and a salt thereof and one or more kinds of specific anions selected from the group consisting of SO42−, NO3−, PO43−, and BO33−. In a case where the chemical solution contains one kind of the specific anion, a content of one kind of the specific anion is 5 ppb by mass to 1% by mass with respect to a total mass of the chemical solution. In a case where the chemical solution contains two or more kinds of the specific anions, a content of each of two or more kinds of the specific anions is equal to or lower than 1% by mass with respect to the total mass of the chemical solution, and a content of at least one of two or more kinds of the specific anions is equal to or higher than 5 ppb by mass with respect to the total mass of the chemical solution.