To provide a lead concentration determination reagent which realizes accurate determination of the lead concentration of a sample solution in a simple manner with safety, even when the sample solution contains zinc ions, and a lead concentration determination method making use of the reagent. The lead concentration determination reagent contains (A) a porphyrin derivative and (B) at least one species selected from among ethylenediamine-N,N'-dipropionic acid, ethylenediamine-N,N'-diacetic acid, and 1,6-diaminohexane-N,N,N',N'-tetraacetic acid.