A wavelength conversion structure and a projection device are provided. The wavelength conversion structure is disposed on a transmission path of an illumination light beam emitted by a light source of the projection device, and includes a rotary disc, a wavelength conversion material, and a scattering-reflective material. The rotary disc has a light-conversion region and a non-light-conversion region. The light-conversion region surrounds the non-light-conversion region. The wavelength conversion material is disposed on the rotary disc, and is aligned to the light-conversion region. An energy gap of the wavelength conversion material is smaller than photon energy of the illumination light beam. The scattering-reflective material is disposed on the rotary disc, and is aligned to the light-conversion region and not aligned to the non-light-conversion region. An energy gap of the scattering-reflective material is larger than the photon energy of the illumination light beam.