A heat dissipating assembly of M.2 expansion card is adapted to fix an M.2 expansion card to a motherboard, and includes a heat dissipating body having a first end and a locking member. The heat dissipating body includes a fixed portion located at the first end and at least one screw hole, and the heat dissipating body is adapted to be fixed to the motherboard through the fixed portion. The locking member is detachably disposed on the at least one screw hole, and the locking member is adapted to fix the M.2 expansion card to the heat dissipating body.