A thermosetting adhesive composition and thermosetting adhesive sheet capable of obtaining stable conductivity even in high-temperature environments or high-temperature/high-humidity environments are provided. The thermosetting adhesive sheet comprises an acrylic copolymer obtained by copolymerizing 55 to 80 wt % of alkyl (meth)acrylate, 15 to 30 wt % of acrylonitrile, and 5 to 15 wt % of glycidyl methacrylate; an epoxy resin; an epoxy resin curing agent; and a dendritic conductive filler having a tap density of 1.0 to 1.8 g/cm3. Thereby, thermal expansion after curing is suppressed, and electrical contacts of the conductive filler are increased, allowing stable conductivity to be obtained even in high-temperature environments or high-temperature/high-humidity environments.