Size reduction is essential to utilize biomass in many applications. Production of fine particles from biomass chips is usually performed using milling machines that consume large amount of energy. Steam explosion (SE) is a promising method for reducing the size of biomass using less energy consumption because it utilizes thermal energy. In this study, we focused on the possibility of the SE method to produce fine particles with a size below 1 mm from wood chips. Sakura (Prunus spp., hardwood) and Japanese cedar (Cryptomeria japonica, softwood) chips with a size of 5-10 mm were used in this study. The effects of SE conditions - such as temperature and residence time - and of the biomass type on the biomass size reduction were investigated in detail. The energy consumption of SE was also calculated and compared with that of the conventional mill. We found that SE is an energy-efficient method for biomass milling. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.