The effectiveness of chemical comminution by liquid ammonia in fragmentation of two lignites, from the area of Ptolemais in Greece, was determined. The resulting distribution of particle sizes, ash, sulfur, nitrogen and thermal energy values were compared with those from conventional mechanical grinding. Results showed that both coals could be selectively comminuted on exposure to liquid ammonia, reaching an apparent steady state with impregnation time. The method had the advantage of producing less fines, a similar liberation of ash and a significantly higher liberation of sulfur, at a given size consist. Some of the nitrogen of the coals retained after treatment could be removed by washing with hot water.