A light guide element and a light source device using the same are provided. The light guide element has a main body. The main body has a hollow portion with a cone shape and a microstructure pattern formed on the main body. The cone-shaped hollow portion has a bottom portion and a top portion. The bottom portion is located on the bottom surface of the main body, and has a first hollow cross section area. The top portion is opposite to the bottom surface, and has a second cross section area smaller than the first cross section area. The microstructure pattern includes high-density areas and low-density areas to improve a light distribution caused by the cone-shaped hollow portion. The light source device includes the light guide element and a ht emitting diode (LED). The LED is used to emit light into the cone-shape hollow portion through the bottom portion.