Abstract: The pathogen which causes cinnamon die back was identified as Botryodiplodiatheobromae. Monospore culture showed that 204 out of 248 clonies were grey incolour, and the other 44 were black. Based on the difference exhibited in pathoge-nicity. growth rate, reaction to boron, illuminance, production of pigment and resultsof electrophoresis of superoxide dismutase (SOD) and protein, it is suggested that twodifferent physiological race existed, and were labeled as Aand B respectively.