A fastener for a heat-dissipating device is adapted to secure a heat sink on a securing seat. The fastener includes a fastening arm having a plate body and a coupling member adapted to couple with one positioning member of the securing seat, a fastening member disposed spacedly below the plate body opposite to the coupling member and adapted to couple with another positioning member, and two linkage sets. Each linkage set is disposed between the plate body and the fastening member, and includes first and second resilient connecting elements connected respectively to the plate body and the fastening member. The linkage sets are pivotable toward each other to cause the plate body to displace toward the fastening member such that the linkage sets engage two openings in the securing seat.