AbstractPlant extracts and other plant products have been used as an alternative to synthetic fungicides or an additional way to reduce their use. The choice of plant extracts and their application depends on their functional characteristics, availability, cost‐effectiveness, and their impact on phytopathogens, and also on the environment. Therefore, the present study aims to assess the potential of Celtis australis methanolic extracts as source of compounds with antifungal activity. Methanolic extracts prepared from leaves and unripe mesocarps of C. australis collected from different localities of Montenegro (Podgorica—PG, Donja Gorica—DG, and Bar—BR) were evaluated for their phenolic compounds' composition as well as antifungal and cytotoxic properties. Obtained results revealed that extracts contain various bioactive constituents including phenolic acids, flavonoids, and their derivatives. The predominant phenolic acid was ferulic acid, identified in leaf samples from DG (187.97 mg/100 g dw), while isoorientin was the most abundant phenolic compound found in all examined samples. Regarding antifungal potential of the tested samples, all but one (prepared from mesocarp BR) possessed higher activity than Previcur, a commercial systemic fungicide intended to control seedlings. In vitro studies on HaCaT cell line showed that the extracts had no toxic effect toward the tested cell line. These results lead to the conclusion that methanolic extracts of C. australis can become an alternative to the use of synthetic fungicides in agriculture. Those extracts represent natural biodegradable fungicides and enable more efficient control of pathogenic fungi.