Time dependence of excited state decay is studied theoretically. The model system is assumed to consist of two electronic levels coupled to a single vibrational mode and dissipating its energy to a thermal bath. The form of inter-state coupling is assumed to be either a) constant (independent on vibrational coordinate) or b) linear in vibrational coordinate. Generally, the rate of excited state decay resonantly increases when the ratio r of the excitation energy and vibrational quantum takes integer values (r = 1, 2, 3, ...). The effect is stronger and appears even for r >= 2 when the Huang-Rhys factor is larger and/or the inter-state coupling is explicitly dependent on vibrational coordinate.