Abstract: Three self-sintered graphite blocks (SGs) were prepared from green pitch cokes with different average grain sizes (5.1, 3.1 and 1.9 μm) using cold isostatic compaction. The microstructures and properties of the SGs were characterized by XRD, SEM, mercury porosimetry, mechanical and thermal tests. Results indicated that the microstructures and properties of the SGs were closely related to the green coke granularity. When decreasing the average grain size of the green coke from 5.1 to 1.9 μm, the density, mechanical properties, Shore hardness and coefficient of thermal expansion increased while the degree of graphitization, crystallite diameter, thermal conductivity, median pore diameter and porosity decreased. The median pore diameters of the SGs were all in the nanometer range, which implied that they could effectively inhibit the infiltration of molten salt and might be used in molten salt reactors.