Fluorescence of ethylcarbazole doped in PMMA polymer films is quenched by an external electric field in the presence of dimethyl terephthalate, indicating that the rate of the intermolecular electron transfer from a photoexcited molecule of ethyl carbazole to dimethyl terephthalate is enhanced by an applied electric field. The field effect on the electron transfer as well as the transfer rate at zero field increases with a decrease of the electron donor-acceptor distance. The free energy change of the electron transfer reaction from photoexcited ethylcarbazole to dimethyl terephthalate is estimated to be about -0.7 eV in PMMA polymer films, based on the external electric field effect on fluorescence intensity of ethylcarbazole combined with the fluorescence lifetime. The molecular polarizability of fluorescent exciplex formed in a mixture of ethylcarbazole and dimethyl terephthalate is also estimated, based on the Stark shift of the exciplex fluorescence.