Radical cations of traps-stilbene and substituted trans-stilbenes (stilbenes and the radical cations denote S and S.+, respectively) were generated from the resonant two-photon ionization (TPI) in acetonitrile with irradiation of one-laser (266- or 355-nm laser) and with simultaneous irradiation of two-color two-lasers (266- and 532-nm or 355- and 532-nm lasers) with the pulse width of 5 ns each. The formation yields of S.+, the TPI efficiency, depended on the properties of S in the lowest and higher singlet excited state (S(S-1) and S(S-n)), generated from one-photon excitation with 266- or 355-nm laser and from two-photon excitation with simultaneous irradiation of 266-and 532-nm or 355- and 532-nm lasers, respectively. The TPI efficiency using two-color two-lasers increased compared with that using one-laser. It is confirmed that the TPI proceeds through two-step two-photon excitation with the S-0 -> S-1 -> S-n transition. In addition to the electronic character of S(So) which depends on the substituent of S, oxidation potential, and molar absorption coefficient of the S-0 -> S-1 absorption as well-known important factors for the TPI efficiency, it is shown that properties of S(S-1) and S(S-n) such as lifetimes, electronic characters of S(S-1) and S(S-n), molar absorption coefficient of the S-1 -> S-n absorption, and ionization rate from S(S) are also important.