Abstract: A double layer mug includes an outer layer, an inner layer, an annular ring, and a grip. The outer layer is transparent, having an engage member on an outer surface. The inner layer can endure high temperature, having an inner annular projection. Between the outer and the inner layer is formed a hollow layer for storing a cool agent therein. The annular ring has an annular aperture for an elastic ring to fit therein, and an inner inner wall and an outer wall defining the aperture contact with an upper mouth of the inner and the outer layer, with an annular groove formed in the inner wall to engage with the inner annular projection, with an engage member of the annular ring engaging the engage member of the outer layer. Thus, the double layer mug can endure very high temperature and has its hollow layer visible through the outer layer.