Commercial nitromethane has an approximate purity of 91.5 mole percent. It was not possible to remove the impurities by simple fractionation and washing with aqueous solutions of silver nitrate and sodium bicarbonate. The most successful procedure was a combination of washing, fractionation, and fractional slow melting. The purity of the nitromethane was followed by freezing point determinations using a platinum resistance thermometer. The highest purity achieved by this method was 99.9 mole percent.