Directional dark matter search experiments enable us to reveal the presence of Weakly Interacting Massive Particles. A promising detector for a directional measurement is a fine-grained nuclear emulsion consisting of fine crystals of silver bromide with 20nm or 40nm size. A critical task for the success of the experiment is to remove background tracks of electrons coming from stopping beta rays of 14C decays in the nuclear emulsion. An electron rejection power of at least 10−10 is needed in order to start a 10kg experiment.We present a novel cryogenic approach to reject the electron background that makes use of the phonon effect in nuclear emulsion. For the proof of principle, we have been investigating the sensitivity of fine-grained nuclear emulsions as a function of temperature by exposing to gamma rays and ion beams with an ion implant system in the range of 77–300K. Results of gamma ray exposure indicate that the electron rejection power is estimated to be better than 3×10−9 at 77K. Results of ion exposure imply that fine-grained nuclear emulsion is sensitive to ions which are light and heavy and ion tracks' angle can be measured.