The contact charging of ionomer-polymer blends was studied by the scanning Kelvin probe. The blends which contain ionomers with mobile ions produced a strong change in its surface potential after contact with an unbiased Pt/Ir tip. The signal on the contacted area decayed slowly with time. The decay was more rapid with the films containing more ions. The magnitude of the charge in the surface potential was found to scale linearly with the film thickness indicating that the charge is localized near the surface. In contrast, only a very weak signal was produced with the films which contained no ions or no mobile ions (e.g., films with both ions covalently bonded to the polymer). These results support previous reports that ion transfer is important in contact charging and the proposal that the resulting charge is primarily a surface phenomenon.