When solid metals are melted, the crystal structure breaks down, and the atomic arrangement becomes entirely random. It is presumed that when metals are in a molten state valence electrons, moving about in an irregular potential field due to the random distribution of ions, behave as free electrons. As one of the experimental methods for examining this hypothesis the measurement of the Hall coefficient of molten metals was undertaken. High purity Cd In, Sn, and Bi were used for the measurement. All of these, metals showed negative Hall cofficients independent of temperature in the molten state and the measured Hall coefficients were in good agreement with the theoretical values calculated under the assumption that in molten metals all of the valence electrons of the atoms contribute to the conduction as free electrons.