The authors propose the following method for preparation of tin difluoride free from tin(IV) and oxygen. Tin(II) oxide is dissolved in cold concentrated hydrofluoric acid. The solution is cooled and filtered to remove insoluble impurities. The transparent filtrate is heated for 1. 5-2 h in a vitreous-carbon crucible in presence of metallic tin. The HF level is maintained constant during the heating. It is found that as tin(II) fluoride is a unipolar fluoride-ion conductor, its purity can be conveniently determined by conductivity measurement. The quality of the synthesized product can be estimated from its conductivity determined with the aid of standard ac bridge circuits. The conductivity of nominally pure SnF//2 samples is (7-9)//19 10** minus **8 OMEGA ** minus **1 multiplied by (times) cm** minus **1 at 293 K. This value may vary within 7%, depending on the method of preparation of the samples for conductivity measurements and on the electrode material. The novel synthesis method developed by the authors can be used for production of large amounts of tin(II) fluoride and may serve as the basis for development of an industrial process for production of high-purity SnF//2 and high-conductivity fluoride-ion SEL based on it.