We measured the pre-melting behavior of an ionic liquid, [i-C(3)mim] Br, using a laboratory-made differential scanning calorimeter with nanowatt stability. A hitherto unknown behavior, intermittent crystallization, was clearly observed in the returning process of the premelting at a cooling rate as slow as 0.05 mK/s. This phenomenon occurred piece by piece in the time scale of 10(2) s in each domain containing similar to 10(14) ion pairs. By combination with our Raman spectroscopic study on the conformational changes of the [i-C(3)mim](+) ion, we interpret this behavior as the crystallization of locally melted domains composed of different conformers, which significantly hinders the crystallization. (C) 2008 Elsevier B.V. All rights reserved.