A wide variety of inorganic constituents were deposited in several units of the NEDOL coal liquefaction pilot plant with a capacity of 150 tons per day. The inorganic constituents were analyzed by CCSEM, XRD and XRF. In the first liquefaction reactor, the growth of crystalline quartz and the interaction of calcium with mineral and/or catalyst were observed to be significant. The inorganic particles of larger size (> about 100 mum) were accumulated in the first liquefaction reactor while the smaller particles were flushed out to downstream. The small catalyst particles were mainly accumulated in the high-temperature separator and the other interacted particles were mainly accumulated in the outlet pipe after letdown valve.