Abstract: ObjectiveThe pathogen causing leaf spot disease on muskmelon in greenhouse in Guangxi in recent years was clarified to provide reference for the effective control of the disease.MethodThe pathogenic fungi were isolated by single spore isolation method from leaves of diseased muskmelon.The pathogenicity of pathogenic fungi was verified by inoculation of detached leaves.Furthermore,the colony,conidiophores and conidia characteristics of the pathogen were observed.Homology analysis on rDNA-ITS gene sequences of the pathogenic fungi was conducted.ResultThe morpho-logical characteristics of the pathogen were consistent with Cercospora citrullina. And its rDNA-ITS gene sequences showed 99% similarity with C. citrullina. Based on the morphological and molecular characteristics,the pathogen was identified as C. citrullina.ConclusionThe serious leaf spot appeared on muskmelon in greenhouse in Guangxi these years is caused by C.citrullina.It is a new disease on muskmelon in Guangxi.