For the polarographic determination of tin in the presence of tungsten, a supporting electrolyte of 5±0.5N hydrochloric acid is recommended. In 6N,8N and 10N hydrochloric acid media, the half-wave potentials of tungsten are-0.71v,-0.65v and-0.61v vs. S. C.E. respectively, all of them are virtually coincident with those of tin wave. However, in 5±0.5N hydrochloric acid media, large portion of tungstic acid precipitates and the half-wave potential of the trace tungstic acid remaining in the solution shifts to a more negative value of-0.75v vs. S.C.E.,whilc that of tin in the same media remains at-0.58v vs. S.C.E.. Hence the interference of tungsten becomes negligible.