We report the experimental evidence of the one-photon resonance in the cationic excited state of cyclopentanone using the femtosecond time-resolved pump-probe method. The transients of the parent ion and the C2H4+ fragment exhibit constant depletion in the pump-probe delay time up to 7 ps, however, that of the C4H8+/C3H4O+ fragment presents formation behavior. By recording dependence of the ion yields as the probe laser intensity, we demonstrate one 400-nm photon resonance in the cationic excited state, which is assigned as the D-4((2)A) cationic state based on the theoretical calculations. Possible dissociation mechanism of the D-4 state is also discussed. (C) 2016 Elsevier B.V. All rights reserved.