© ACRA 2018 - 9th Asian Conference on Refrigeration and Air-Conditioning. All rights reserved. Heat exchangers which are operated at 0 deg.C below are subjected to occurring frost deposition and its growth on the cold surface because of being exposed to humid air. The structure of frost is porous consisting of ice crystal and air, which makes the thermal conductivity of frost remarkably low. Therefore, frost formation causes serious problem on the heat transfer performance of the heat exchanger. In this study, the three dimensional distribution of the frost deposition and the frost density profiles on the plate-fin tube heat exchanger are quantitatively measured by using the neutron computed tomography. 600 projection images are taken by the neutron radiography with rotating the heat exchanger through 180 degrees. The reconstructed images of the computed tomography show clearly the three-dimensional frost deposition distribution on the heat exchanger. At the fin edge, high frost deposition are observed, however, the frost layer was hardly seen in the wide area of the wake region. The frost density profile on the fin surface can be estimated from the reconstructed neutron computed tomography.