The excitation spectrum of the photosynthetic reaction center (PSRC) of Rhodopseudomonas (Rps.) viridis is assigned by using the SAC(symmetry adapted cluster)-CI(configuration interaction) method. All the chromophores included in the PSRC, bacteriochlorophyll b dimer (special pair, P), bacteriochlorophyll b in L- and M-branches (B-L and B-M), bacteriopheophytin b in L- and M-branches (H-L and H-M), menaquinone (MQ), ubiquinone (UQ), and four different hemes, c-552, c-554, c-556, and c-559 in c-type cytochrome subunit, were calculated within the environment of proteins, waters, and the other chromophores which were dealt with by the point-charge electrostatic model. We have assigned successfully all the peaks in the experimental spectrum in the energy range from 1.2 to 2.5 eV. The assignment was done by comparing the SAC-CI theoretical spectrum with the experimental one in excitation energy, oscillator strength, linear dichroism data (angle of transition moment), and other experimental information available. Almost all the peaks were red shifted due to the effect of proteins. The present assignment of the spectrum would give a basis for future photoexperimental studies of the PSRC.