The invention provides a wavelength conversion device and a projection device, where the wavelength conversion device includes a substrate, a wavelength conversion layer, and a light-transmitting layer. The wavelength conversion layer is disposed on the substrate and is made of a wavelength conversion material and a bonding material. The wavelength conversion layer has a refractive index of 1.55-1.70. The light-transmitting layer is disposed on the wavelength conversion layer and is made of the bonding material. The wavelength conversion device and the projection device provided by the invention have greater brightness and are less restricted by temperature during operation.