Provided is a thermosetting resin composition including an inorganic filler and a thermosetting resin matrix component, in which the inorganic filler includes secondary sintered particles each formed of primary particles of scaly boron nitride, and at least some of the secondary sintered particles each have a maximum cavity diameter of 5 μm to 80 μm. The thermosetting resin composition can be used for providing a heat conductive sheet in which electrical insulation property is kept by controlling where the defects such as voids and cracks occur and their size, and which has excellent heat conductivity.