Abstract: Botryodiplodia theobromae has been identified as a cause of dei back ofCinnamom in Guang Dong.The occurreuce of the disease was closely related to in- jury caused by Thymiatris sp.and the defficiency of boron in thesoil.Preci-pitation and high humidity were crucial for sporogensis and dispersal when thetemperature was appropriate.The application of cartap,chlorothalonil boron andcupric sulfate around the root,and spraying fenvalerate and chlorothalonilsimultaneously proved to be effective in controlling the disease.