The ion exchange of strontium hydroxyapatite (SrHAp) with Pb2+ has been investigated under acidic conditions at 293 K. The addition of various acids to the exchanging solution enhanced the exchange capacity in the order HCl > HBr > HF > HNO3 > no acid, corresponding to the formation of halogen apatites with the former three acids or hydrogen phosphate with HNO3. Since the ion-exchange capacity of SrHAp under nonacidic conditions is higher than that of chlorapatite, the aforementioned observations can be attributed to the participation of the protons introduced by the acids.