In NEDOL's 1-ton-per-day process supporting unit, a plant designed to provide support data for the NEDOL coal liquefaction process which has been developed up to the 150-tons-per-day scale, the hydrodynamic behavior of coal slurry in the coal liquefaction reactors was observed using neutron absorption tracer equipment. The results clarified that the three reactors installed in series in the plant performed in a complete mixing mode providing sufficient contact between the liquid and hydrogen gas. It was also found that the increase of the gas feed rate resulted in the increase of liquid-phase mean residence time (MRT). This increase of MRT resulted in a decrease in the coal liquefaction residue yield and an increase in the coal liquefaction oil yield. However, the increase of the MRT did not improve the naphtha (C-4-493 K fraction) yield because of vaporization of the light oil (493-623 K fraction) in the coal liquefaction reactors.