  In this talk, we introduce an effective chiral action, derived from the
instanton QCD vacuum configuration, in order to study the modification of
mesonic properties in medium. We present our recent theoretical results on the
electromagnetic from factor and rho-meson mass shift at finite density. We
observe that the rho-meson mass is dropped by about 10%: m*_rho/m_rho ~ 1-0.12
mu_B/mu_0, which is compatible with that estimated by the QCD sum rule as well
as by Brown and Rho.
