Dielectric spectroscopy of E.coli cell before and after exposure to heavy metals Cd2+,Cu2+, Zn2+ and Ca2+ was investigated. The results indicate that changes in dielectric spectra reflect effects of heavy metal on the structure and function of E.coli cells. Heavy metal can change membrane capacitance as well as permittivity and conductivity of the cytoplasm. Changes in volume fraction suggested that dielectric measurement could monitor the growth of E.coli cells. These results demonstrated that dielectric spectroscopy was a potential effective technique for studying electric properties of biological cells.