The antifungal activity of cork tree extract against three plant pathogenic fungi (Colletrotrichum gloeosporiodes (Penz.) Penz. & Sacc., Pythium ultimum Trow. and Botrytis cinerea Pers.) was investigated antifungal active substances were identified. Cork tree extract showed concentration-dependent antifungal activity against three plant pathogenic fungi. The cork extract had antifungal activity in a concentration-dependent manner, and in particular, showed the most vigorous antifungal activity against Botrytis cinerea. In cork tree extract, the incidence of strawberry powdery mildew fungus after 7 days of treatment was significantly lower as the treatment concentration increased. Control value against strawberry powdery mildew fungus was 49% of cork tree extract, 69% of berberine chloride, and 67% of berberine bromine, which was lower than 80.5% of Rifzol, a representative antifungal compound, but showed strong antifungal activity. The isolated compound and berberine derivative showed similar effects to Rifzol at the treatment concentration (75 μg/ml), and a concentration of at least 10 μg/ml of fresh weight showed a preventive effect against strawberry powdery mildew fungus. Fractions showing antifungal activity were obtained by TLC, and each fraction was examined for the antifungal activity to obtain fractions showing antifungal activity against three types of pathogenic fungi. The compound isolated through TLC analysis was analyzed by HPLC equipped with an ODS column to obtain the main peak presumed to be berberine, which was confirmed as a berberine through 1H NMR analysis. The results of this study are expected to be utilized as biological pesticides with strong antifungal activity against plant powdery mildew etc.