The present invention provides an illuminating device and heat-dissipating structure thereof. The heat-dissipating structure includes a plurality of heat-dissipating units stacked together. Each heat-dissipating unit includes a cone-like portion with an opening and a plurality of protrusions connected to the cone-like portion, wherein at least one of the protrusions of one heat-dissipating unit is coupled to that of the adjacent heat-dissipating unit to form one or more zonal planes for allowing a light source to be disposed thereon to constitute the illuminating device, and the openings of the heat-dissipating units are liked together to form an airflow passage.