Abstract: In order to identify the causal agent of black spot disease on wax apple (Syzygium samarangense Merr.et Perry) in its taxonomic status, the causal fungi FJAT-9860 was isolated and characterized with pathogenicity test, morphology and culture feature observation, rDNA-ITS sequences assay and biological characteristics test.The results indicated that the causal agent belong to Lasiodiplodia theobromae.The colony of strain FJAT-9860 on PDA was white at first, then gradually became as grey to black.The monadic conidia were elliptic to round, and colourless.The rDNA-ITS sequence of the strain shared 99%identity with that of Lasiodiplodia theobromae strain.The results showed that the optimum temperature for mycelium growth of this pathogen was 25℃and the optimum pH was 8.0.The mycelial growth was affected by different carbon sources and the best one was mannitol.