The present invention relates to novel trifluoromethyloxadiazoles of the formula I,or the N- oxides, or the agriculturally useful salts thereof; and to their use for controlling phytopathogenic fungi; and to a method for combating phytopathogenic harmful fungi, which process comprises treating the fungi, the plants, the soil or seeds to be protected against fungal attack, with an effective amount of at least one compound of the formula I,or an N-oxide,or an agriculturally acceptable salt thereof; and to agrochemical compositions comprising at least one compound of the formula I;and to agrochemical compositions further comprising seeds.