  The annihilation poles for the form factors in XXZ model are studied using
vertex operators introduced in \cite{DFJMN}. An annihilation pole is the
property of form factors according to which the residue of the $2n$-particle
form factor in such a pole can be expressed through linear combination of the
$2n-2$-particle form factors. To prove this property we use the bosonization of
the vertex operators in XXZ model which was invented in \cite{JMMN}.
