We measured longitudinal and transverse relaxation times (T-1 and T-2) of 1-butyl-3-methylimidazolium bromide ([bmim] Br) from 203 to 393 K, using pulse H-1 NMR. T-1 and T-2 data show the existence of liquid, super-cooled liquid and 'coagulated state'. The coagulated state appears only in the cooling process at the temperature where [bmim] Br will crystallize in the heating process. The activation energy for rapid reorientational motions of the alkyl groups in the crystalline state was determined to be 13.3 kJ mol (1). By the T-2 measurement, it was confirmed that very slow reorientational molecular motions of the overall [bmim](+) begin near the crystallizing point. (C) 2008 Elsevier B.V. All rights reserved.