An illuminating device comprises a heat sink, at least one light emitting module and a speaker. The heat sink has a first containing space, a second containing space and a first channel being in communication with the first containing space and the second containing space. The light emitting module is arranged in the first containing space and contacted with the heat sink. The speaker comprising a thin film is arranged in the second containing space. When the speaker is in operation, the thin film vibrates so that a first airflow from the second containing space to the first containing space through the first channel is formed. In the above-mentioned illuminating device, the vibration of the thin film of the speaker causes air in the first containing space to flow, and the heat dissipation efficiency of the illuminating device is improved.