Abstract: Traditional pathogen isolation method was time consuming, laborious and with low success rate. In order to improve the isolation efficiency, a selective medium was developed for the isolation of Phyllosticta commonsii under non-sterile environmental conditions. PSA containing streptomycin sulfate (50 μg/mL) was used as the basal medium. Carbendazim, fosetyl-aluminum and mancozeb with different concentrations were employed as additives. Results from orthogonal experiments showed that the suitable concentrations of carbendazim, fosetyl-aluminum and mancozeb in selective medium were 0.5 μg/mL, 100-200 μg/mL and 3.125-12.5 μg/mL, respectively. Although the selective medium can effectively inhibit the growth of three common interferefering fungi, Penicillium variabile, Aspergillus niger, and Alternaria tenuissima, it has little effect on the growth of macular pathogen, which implied that it could be used to isolate P. commonsii from the diseased blades of peony.