An LED illuminating device includes a heat sink, a first substrate, a second substrate and a connector. The heat sink comprises a first end, a second end opposite to the first end along the axial direction of the heat sink. The first substrate mounted on the first end, the second substrate mounted on the second end, the second substrate has a size smaller than the first substrate. Heat generated by the first substrate is transferred to air and will not accumulate and be transferred to the second substrate. Additionally, because the first substrate and the second substrate are spaced by the heat sink, the heat radiation efficiency is improved.