Northern corn leaf blight, caused by the fungus Exserohirum turcicum Pass. (Leonard and Suggs), is one of the major diseases in most corn-growing areas of the world. Research on gene tagging of E. turcicum has been limited due to the lack of an efficient transformation system. Since E. turcicum produces and accumulates melamin in cell walls during vegetative growth, it is difficult to efficiently isolate its protoplast. To isolate the protoplast of this pathogen with a high frequency, the effects of cell wall degradation enzymes, including beta-1,3-glucanase (Fungase, Funcelase, Novozyme and Glucanex) and beta-glucuronidase (Driselase, Uskizyme and Kitalase), enzyme concentrations, combinations, strains and medium on the isolation frequency were tested. The isolation frequencies were high enough for transformation when the combinations of (Kitalase + Glucanex + Driselase), (Kitalase + Glucanex) or (Kitalase + Uskizyme) were used. Moreover, the isolation frequencies of protoplast were significantly affected by the cultural morphologies of strain and the growth stage of mycelia. Among the plasmids tested, only plasmid pAN71 is efficient for transformation of E. turcicum. This result will provide some useful information for gene tagging of E. turcicum and other species in Exserohirum.