Polyprenyl derivatives having the formula ##STR1## [wherein A and B individually represent a group of the formula --CH.sub.2 OR.sup.1 (wherein R.sup.1 is hydrogen atom, an alkyl group having an intervening hetero atom in the carbon chain, carboxyl group on its salt or an aliphatic acyl group optionally having an intervening hetero atom in the carbon chain, an aromatic acyl group, a heterocyclic acyl group, an araliphatic acyl group, a heterocyclic aliphatic acyl group or a radical of an inorganic acid or its salt) or where one of A and B represents the group --CH.sub.2 OR.sup.1, the other represents a group of the formula --COOR.sup.2 (wherein R.sup.2 represents hydrogen atom, a metal atom capable of forming a salt, an organic base or an akyl group), a group of the formula ##STR2## or a group of the formula ##STR3## (wherein R.sup.3 and R.sup.4 may be the same or different and each represents hydrogen atom, an alkyl group optionally having a heterocyclic substituent, an aryl group or an aralkyl group or R.sup.3 and R.sup.4 may jointly form a ring optionally containing other hetero ring atom) and n is an integer of 0 to 4 inclusive, provided that when both A and B are the group --CH.sub.2 OR.sup.1, either of the R.sup.1 represents an alkyl group having an intervening hetero atom, carboxyl group or its salt, an aliphatic acyl group having an intervening hetero atom in the carbon chain, a heterocyclic acyl group, a heterocyclic aliphatic acyl group or a radical of an inorganic acid or its salt]. These derivatives are useful as medicines for treating peptic ulcer.