An illumination system including a beam splitter, a first lamp, a second lamp, a first reflector, a second reflector, and a light uniforming element is provided. The first and the second lamp emit a first beam and a second beam to the beam splitter, respectively. A part of the first beam reflected by the beam splitter and a part of the second beam passing through the beam splitter constitute a third beam, and the other part of the first beam passing through the beam splitter and the other part of the second beam reflected by the beam splitter constitute a fourth beam. The first reflector and the second reflector reflect the third beam and the fourth beam, respectively. The light uniforming element is disposed on transmission paths of the reflected third beam and the reflected fourth beam.