Theory of excitation transfer in the intermediate coupling case is proposed. This theory is appropriate to such molecular: systems where the interaction between donor and acceptor is considerably strong so that the excitation transfer takes place before the thermal equilibrium is attained in the excited intermediate state of the donor but is not so strong as the exciton mechanism holds true. The expected remarkable properties of the intermediate coupling excitation transfer are that there exists a concurrent process of the superexchange mechanism and the sequential mechanism in the same way as the electron transfer reaction. We have proposed a new method of evaluating the degree of sequentiality which bases on much physical background, namely counting the fi act-ion of density flow passing through the intermediate state.