The invention provides a wavelength conversion device and a projection device including the same. The wavelength conversion device includes a substrate, a reflective layer, and a wavelength conversion layer. The reflective layer has different thicknesses in a radial direction of the substrate. The invention further provides another wavelength conversion device and another projection device including the same. In the wavelength conversion device, the reflective layer includes a first colloid and reflective particles distributed in the first colloid. The reflective layer includes an inner reflective layer, a central reflective layer and an outer reflective layer. The concentration of the reflective particles in the central reflective layer is different from the concentration of the reflective particles in the inner reflective layer and the concentration of the reflective particles in the outer reflective layer. The invention can improve the heat dissipation of the wavelength conversion layer, and improve the conversion efficiency.