A light emitting diode (LED) device includes a stacked epitaxial structure, a heat-conductive plate and a seed layer. The stacked epitaxial structure sequentially includes a first semiconductor layer (N—GaN), a light emitting layer, and a second semiconductor layer (P—GaN). The heat-conductive plate is disposed on the first semiconductor layer, and the seed layer is disposed between the first semiconductor layer and the heat-conductive plate. Also, the present invention discloses a manufacturing method thereof including the steps of: forming at least one temporary substrate, which is made by a curable polymer material, on an LED device, and forming at least a heat-conductive plate on the LED device.