The essential oil composition of the moss Rhodobryum ontariense obtained by hydrodistillation was preliminary analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Thirteen compounds (86.41 of the total oil) were identified. The main chemical constituents were phytol (31.95) and 1-octen-3-ol (15.44). Such an abundance of phytol has not yet been reported in other mosses. Four chemicals (cis-decahydronaphthalene, allo-hedycaryol, jasmone and 2,5,5,8a-tetramethyl-1,4,4a,5,6,7,8,8a-octahydronaphthalene-1-carboxylic acid, methyl ester) are first records, not only for the genus Rhodobryum and mosses in general, but also for the group of bryophytes as a whole.