  The pion electromagnetic form factor at finite temperature is studied using
an effective chiral lagrangian that includes explicitly vector mesons. We find
that in the time-like region around the rho meson resonance it decreases with
increasing temperature and leads to a suppression of dilepton production from
pion-pion annihilation in a hot hadronic matter. Effects on dilepton production
in high energy heavy ion collisions and its relevance to the phase transition
in a hot hadronic matter are discussed.
