Polyprenyl derivatives having the formula ##STR1## in which R.sup.1 and R.sup.2 may be the same or different and each represents hydrogen atom, hydroxyl group, an alkoxy group having 1-8 carbon atoms, an aliphatic acyloxy group having 2-18 carbon atoms, an aromatic acyloxy group or an araliphatic acyloxy group having 2-3 carbon atoms in the aliphatic acyl moiety, R.sup.3 represents hydrogen atom, an alkyl group having 1-8 carbon atoms, an aliphatic acyl group having 2-18 carbon atoms, an aromatic acyl group or an araliphatic acyl group having 2-3 carbon atoms in the aliphatic acyl moiety, n is an integer of 1-4 and, when n is an interger of 2-4, R.sup.2 's may be the same or different; provided that, when n is 1 or 2, at least one of R.sup.2 and R.sup.2 's is hydroxyl group, an alkoxy group, an aliphatic acyloxy group, an aromatic acyloxy group or an araliphatic acyloxy group. These derivatives are useful as medicines for treating peptic ulcer.