A new principle of tin refining in molten electrolytes is proposed. Its main feature is mass transfer between electrodes through a thin porous diaphragm of (0.5-1.0) x 10(-3)m thickness, which is impregnated with molten electrolyte. The distance between the electrodes is equal to the diaphragm thickness. A mixture of zinc chlorides, alkali chlorides and tin chlorides is proposed as an electrolyte, It is shown that thin layer electrolysis makes it possible to produce tin with an impurity content no more than 1 x 10(-3)%. The thin layer electrolysis in melts reduces the specific electrical energy by a factor of 1.5-2.0 and the electrolyte consumption by a factor of 2.5-6.0 per ton of purified tin in comparison with current practice. The results show the proposed method of thin layer electrolysis in molten electrolytes to be promising for tin refining.