A blight disease of carnation (Dianthus caryophyllus L.) caused by Alternaria dianthi was found in greenhouses and vinylhouses in southern Korea. In severely affected beds, many carnation plants were blighted and died. The growth of the fungus id vitro was optimum between 24 and $28^{circ}C$. In controlled inoculations, A. dianthi caused lesions on leaves and stems of carnation plants.