An illumination system and a projection apparatus are provided. The illumination system includes an excitation light source, a light guiding element, a filter module, an optical wavelength conversion module, and a homogenizing element. The light guiding element reflects an excitation beam coming from the excitation light source. The filter module includes a filtering region and receives the excitation beam reflected by the light guiding element. The optical wavelength conversion module includes a wavelength conversion region, receives the excitation beam reflected by the filtering region and reflects a conversion beam converted from the excitation beam. The conversion beam forms at least one color beam after passing through the filtering region of the filter module. The homogenizing element receives the excitation beam coming from the filter module and the at least one color beam. An incident angle of the excitation beam on the light guiding element is θ1, and θ1>0°.