Five Betula species, B. pendula, B. browicziana, B. medwediewii, B. litwinowii, and B. recurvata, were collected from different parts of Turkey. The leaves of these species were hydrodistilled to yield the consequent essential oils. The essential oil compositions were investigated by GC/MS. 14-Hydroxy-beta -caryophyllene was the main constituent in the oil of B. pendula 14-Hydroxy-4, 5-dihydro-beta -caryophyllene, a new compound, was identified as the main constituent in the oils of B. browicziana, B. litwinowii, and B. recurvata. In the oil of B. medwediewii methyl salicylate was the main compound. Various phytopathogenic fungi were studied by the agar tube dilution technique to test the antifungal activities of the essential oils at 400 mug/ml concentration. The essential oils showed strong antifungal activity against Cephalosporium aphidicola, Drechslera sorokinianse, Fusarium solani, and Rhizoctonia cerealis.