Intramolecular photoinduced electron transfer in a series of donor-acceptor systems consisting of 9,10-dimethoxyanthracene and differently substituted benzoic esters have been investigated. From fluorescence life-time measurements using single-photon counting technique, the rate constants of electron transfer ket were obtained. The free energy changes ΔG of electron transfer from the first excited state of 9,10-dimethoxyanthracene were obtained by determining the redox potentials of the donor and the acceptors and the first excitation energy. The dependence of photoinduced electron transfer rates on the exothermicity of the reaction has been studied by the theoretical analysis based on quantum mechanical treatments of electron transfer. The results show that the experimental values coincide well with that obtained by theoretical calculations. Although the inverted region is not seen in our results, the present treatment predicts that the inverted region would be observed at still lower values of ΔG than so far examined.