A water-based composition for treating copper or copper alloy surface for lead-free soldering, the composition comprising a compound represented by general formula (1): ##STR00001## wherein R.sup.1 is hydrogen or methyl, and either R.sup.2 and R.sup.3 represent chlorine and R.sup.4 and R.sup.5 represent hydrogen, or R.sup.2 and R.sup.3 represent hydrogen and R.sup.4 and R.sup.5 represent chlorine.