An add-in module is provided. The add-in module includes a substrate, a plurality of first heat sources, a plurality of second heat sources, a heat sink and a heat-dissipation plate. The substrate includes a first substrate surface and a second substrate surface. The first substrate surface is opposite the second substrate surface. The first heat sources are disposed on the first substrate surface. The second heat sources are disposed on the second substrate surface. The heat sink corresponds to the first substrate surface and is thermally connected to the first heat sources, wherein the heat sink includes a heat-sink base and a plurality of heat-dissipation fins, and the heat-dissipation fins are connected to the heat-sink sink base. The heat-dissipation plate corresponds to the second substrate surface and is thermally connected to the second heat sources.