The research focused on identification the pathogen of Aquilaria sinensis dieback disease and confirmation the function of inducing agarwood formation by fungi.The morphological observation, rDNA ITS sequence analyses, Koch's postulates and pathogenicity test were used to identify the isolates.The isolates of the causal agent was Lasiodiplodia theobromae, which induced the plant to produce highly valuable agarwood.The first report of dieback disease of Aquilaria sinensis caused by L. theobromae, and our research results laid a theoretical foundation for agarwood production by using fungus.