Some crown ethers were found to show significant antifungal activity against some wood-decay fungi, phytopathogenic fungi and eumycetes,Trichophytons for dermatomycosis. Their toxicity was evaluated by the paper disc method as well as by determining the values of ED50, i.e., the concentration which inhibits the mycelium growth by 50%. The fungi examined are Tyromyces palustris, Picnoporous coccineus, Coriolous versicolor, Pyricularia filamentosa, Fusccrium sp., Trichophyton rubrum, Trichophyton sp., etc. Among the 26 crown ethers tested, 3, 5-di-t-butyl-benzo-15-crown-5 showed relatively high activity, the highest ED50 value of which being 8 μM or 3 ppm. Other alkylbenzocrown ethers, dicyclohexyl crown ethers and Kryptofix 22DD also showed considerable activity. On the other hand, unsubstituted crown ethers, benzocrown ethers with a polar substituent, Kryptofix 222B and Kryptofix 221 were inactive.