The present invention relates to an evaporation source for evaporating an organic electroluminescent layer. In particular, the present invention relates to the evaporation source preventing an aperture, through which a vaporized evaporation material is emitted, from being clogged by restricting heat transfer to outward. The evaporation source according to the present invention includes a cell retaining an evaporation material therein; a cell cap installed on the upper part of the cell and having a cell cap aperture for emitting a vaporized evaporation material; an external wall placed in the outside of the cell to support a heating means set up at the outside of the cell; a cover placed above the cell cap, fixed to the upper end of the external wall, and having a cover aperture corresponding to the cell cap aperture; and a shut-off plate placed between the cover and the cell cap and having a shut-off plate aperture corresponding to the cell cap aperture and the cover aperture in the center of the shut-off plate.