Abstract: Provided is a copper-zinc alloy electroplating bath which can form a copper-zinc alloy plating coating having an improved throwing property and a plating method using the same. Also provided is a copper-zinc alloy electroplating bath containing, as an additive, at least one selected from the group consisting of the compounds represented by the following formulae (I) to (III): (wherein R1 represents a lower alkylene group, R2 represents H or a lower alkyl group, and the weight-average molecular weight is 103 to 105); and Na—SO3—(CH2)3—S—S—(CH2)3—SO3—Na (III) These additives can be used alone, and two or more of these can be used in combination.