The assignment of experimental optical absorption spectra of protonated anthracene has been under debate for years. It is complicated by the presence of rich vibronic spectral features and the possible co-occurrence of two isomers, 9H-An(+) and 1H-An(+). In this study, the vibrationally resolved absorption spectra of 9H-An(+) and 1H-An(+) have been calculated using time-dependent density functional theory. The calculated vibronic spectra profiles of 9H-An(+) and 1H-An(+) are in excellent agreementwith the corresponding experimental results and provide unambiguously spectra assignments. It shows that the previously reported assignments based on vertical excitation energy are largelywrong. The onset located at 493.8 nmof the experimental spectrumcan be assigned to the S-0 -> S-1 transition of 9H-An(+), while the origin band located at 453.5 nmcorresponds to the S-0 -> S-2 transition of 1H-An(+).