The purpose of this study is to fabricate single crystals of the solid solution system Pb1-xSnxF2 (x=0, 0.1, 0.2) and to further clarify the correlation between the crystal structure and the ionic conduction by crystal structure analysis and the examination of the frequency dependence of the complex ionic conductivity using an impedance spectroscopy method. The frequency dependence was precisely measured in wide frequency and temperature ranges. The hopping frequency of fluoride ions could then be estimated. It became clear that the activation energy for mobile fluoride ion generation was very small in the system of Pb0.9Sn0.1F2 and Pb0.8Sn0.2F2, and all fluoride ions were mobile. It is suggested that the activation energy, with which fluoride ions hop to adjacent sites, is determined by the bottleneck formed by (Pb2+, Sn2+) ions.