Coking of volatiles generated from coal in pyrolysis has been a focal issue in coal pyrolysis and upgrading of coal tar, but limited work can be found in the literature on evolution of coke in composition and structure under the pyrolysis conditions. This work characterizes the coke formed in reaction of a subbituminous coal tar at 300, 400, and 500 °C in 40 min in a semibatch system which allows natural evaporation of light fractions. The coke is categorized into two types, the one suspended in tetrahydrofuran (THF), coke-S, and the one deposited on the wall of tube reactor, coke-D. It is found that coke-D accounts for 70–85% of total coke. With increasing tar reaction temperature and time the quantity of coke increases from 1.0% to 16.3 wt % and the particle size of coke-S increases from a most probable size of approximately 0.1 to 700–800 μm. This change is accompanied by reduction in alkyl side chains and heteroatoms (O, N, and S), as well as the enrichment in the aromatic Car–Car bond, which lead to ...