An illumination system and a projection apparatus are provided. The illumination system includes an excitation light source, a light combining device, a filter module, and a wavelength conversion module. The light combining device is disposed on a transmission path of an excitation light beam emitted from the excitation light source. The filter module is disposed on a transmission path of the excitation light beam transmitted from the light combining device. The filter module includes a light passing-through area allowing the excitation light beam to pass through and at least one filter area reflecting the excitation light beam. The wavelength conversion module is disposed on a transmission path of the excitation light beam reflected by the at least one filter area. The wavelength conversion module converts the excitation light beam reflected by the at least one filter area into a converted light beam and reflects the converted light beam.