Abstract: An LED light source device with color temperature adjustment capability includes at least one light-emitting diode and a color temperature conversion element. A front end of the light-emitting diode has a light-emitting end. The color temperature conversion element is disposed in front of the light-emitting end of the light-emitting diode. The color temperature conversion element includes a light-transmitting substrate and color temperature conversion materials. The color temperature conversion materials are provided on/in the light-transmitting substrate. The color temperature conversion materials include high refractive index materials and low refractive index materials. The high refractive index materials that are selected from the group consisting of TiO2, Ti3O5 or Ta2O5. The low refractive index materials that are selected from the group consisting of SiO2 or MgF2. The light beam emitted by the light-emitting diode passes through the color temperature conversion element to change its color temperature.