The inhibitory effect of different essential oils on ethylene biosynthesis was investi-gated by using apple (Malus domestica Borkh. cv. Tsugaru) fruit and young peach (Prunus persica Batsch. cv. Nishino-hakuto) seed tissues. Apple tissues retain a high ethylene-pro-ducing capacity, whereas young peach seeds begin to produce ethylene rapidly after being removed from the pits. A more pronounced inhibition of ethylene biosynthesis by the oils was noted in peach seed than in apple fruit tissue. Linalool, citral, citronellal, and 1-octanal inhibited ethylene production. in apple fruit tissues by 50 to 72% over the range of 3.6 to 36 nl•ml-1; citronellol, geraniol, 1-nonanal, β-pinene, p-cymene, and α-pinene were less inhibitory of ethylene production. In the peach seeds, the aldehyde group of essential oils inhibited ethylene production and concomitantly suppressed the in-crease in ACC content by 98 to 100%; alcohol and hydrocarbon groups were less sup-pressive. Most of the essential oils, especially the aldehyde group, seem to inhibit ethylene production by suppressing ACC synthesis.