Dynamic properties of 1-butyl-3-methylimidazolium bromide ([bmim]Br) in D2O were investigated by NMR. The diffusion coefficients of [bmim](divided by)and HDO were determined separately by the pulse field gradient method. The dynamics of Br- was estimated by the half-widths of the signals of Br-81-NMR. The results indicate that an anomalous dynamics, especially for [bmim](divided by), is evident in the region below similar to 0.1 M (0.0019 in the mole fraction of [bmim]Br). For [bmim](divided by) and HDO, maxima appeared in the curves of the diffusion coefficients plotted against the concentration. The relaxation time, T-2, for Br- showed a break in slope at this composition. Probable interpretations on these findings are presented. (c) 2006 Elsevier B.V. All rights reserved.