In wet coal preparation, the products of some processes are transported as low-concentration suspensions. Their rheology is greatly affected by the properties of the coal particles that result from the formation and weathering during preparation. In this study, the properties of coal particles, including volumetric properties (i.e., solids content, granularity, and clay mineral fraction) and surface characteristics (i.e., dynamic potential, degree of coalification, and degree of surface oxidization), were studied to determine their effects on the apparent viscosity of low-concentration coal suspensions. With increasing solids content and smaller particle size in the suspension, the interactions between the coal particles became stronger due to the increased particle content, thus increasing the coal suspension’s apparent viscosity. Adding clay minerals to the suspension gradually changed its composition and structure and increased its viscosity. The dynamic potential of the coal particles and inter-particle electrostatic repulsive forces were reduced with the addition of Ca2+ ions, and the coal particles collided and aggregated, which increased the apparent viscosity of the suspension. For coal with a low degree of coalification or coal had been oxidized by a hydrogen peroxide solution, the suspension of the hydrophilic coal particles was associated with a lower apparent viscosity than that of highly hydrophobic solids, which tended to aggregate and form flocculent masses.