A heat-dissipating mechanism for a motor includes a rotor and a stator base. The rotor rotates with respect to the stator base and includes a casing and a hub. The casing has a side portion and a bottom portion, and at least one opening is disposed at the bottom portion. The hub is disposed on the casing, for preventing an external particle from entering the rotor. The hub includes a plurality of separation ribs and when the hub is disposed on the casing, a heat-dissipating passage is formed between every two adjacent separation ribs and the side portion of the casing.