An illumination device includes a body. The inner space of the body is divided into two parts as a first part and a second part. A heat dissipating module is disposed in the first part. The second part is fully sealed so that dusts, water and insects may be kept off. A plurality of light emitting units are disposed in the second part so as to provide light. The light emitting units are connected with the heat dissipating module in the first part. Hence, heat generated by the light emitting units may be dissipated out of the body and so that the illumination device of the present invention may have a longer service life.