A wavelength conversion device includes a heat dissipation substrate, a first reflection layer, a second reflection layer, and a wavelength conversion layer. The first reflection layer is disposed on the heat dissipation substrate. The second reflection layer is disposed on the first reflection layer. The wavelength conversion layer is disposed on the second reflection layer. The first reflection layer is located between the heat dissipation substrate and the second reflection layer, and the second reflection layer is located between the first reflection layer and the wavelength conversion layer. A reflectivity of the second reflection layer to a visible light is greater than a reflectivity of the first reflection layer to the visible light, and a thickness of the first reflection layer is greater than or equal to a thickness of the second reflection layer. A projection device having the wavelength conversion device is further provided.