A two-dimensional unsteady numerical simulation with a detailed chemical reaction mechanism that considers 158 species and 1804 reactions is applied to pulverized coal combustion in a mixing layer and the soot formation behavior is investigated in detail. The computational conditions and ignition process are the same as those in our previous work (Muto et al., 2017). The results show that the peak of the mass density of the soot is distributed in the region where the gas temperature is higher than the unburned gas temperature of the mixture of volatile matter and air (1300-1400 K) and lower than the flame temperature (2000 K similar to). This is due to the fact that soot formation from the precursors (C2H2 and C6H6) is enhanced as the gas temperature increases, whereas the quantities of the precursors and the produced soot are reduced due to oxidation at the higher gas temperature condition that exists close to the flame. The peak value of the mass density of the soot is also distributed in the region between the peak values of the gas temperature and the probability density function of the number of coal particles. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.