An LED illuminating device includes a light-emitting module, a heat sink and an electrical module. The light-emitting module includes an elongated hollow light penetrable tube and a light source. The heat sink is received in and mounted to the light penetrable tube, and includes an elongated base and a plurality of fins. The light source is thermally attached to a bottom surface of the base. The base and an upper portion of the light penetrable tube cooperatively define a heat dissipation chamber. The fins are accommodated in the heat dissipation chamber. The light penetrable tube defines a plurality of air exchanging holes through the upper portion thereof communicating with the heat dissipation chamber. The electrical module includes at least one circuit board received in the heat dissipation chamber, and two end covers arranged at two ends of the light penetrable tube.