Optical nonlinearities (including nonlinear absorption and nonlinear refraction) and the temporal properties of the nonlinear refraction of hypocrellin A (HA) in its resonant region have been investigated by using single-beam Z-scan and time-resolved two-color Z-scan techniques with picosecond pulses. The reverse saturable absorption effect can be attributed to the efficient absorption of excited states of both the normal and tautomeric forms, S-1 and S-1＇, with the contribution of S-1 as the dominant mechanism. The change of the refractive index of HA increases with increasing irradiance I-0 at low irradiances (<5 GW/cm(2)), while it hardly changes with I-0 at high irradiances. The explanation for such an experimental phenomenon is that the averaged population densities of both S-1 and S-1＇ increase with I-0 at low irradiance, while those of these two states become saturated at high irradiance. The refractive nonlinearities exhibit a very slowly decaying tail, which is attributed to the contributions of S-1, S-1＇, and the triplet state of the normal form, T-1, and is dependent on the rise times and lifetimes of these intermediate states. The kinetic model for HA allows for the determination of the absorption cross sections of the ground state of the normal form of HA S-0, the ground state of its tautomer S-0＇, the excited state of its tautomer S-1＇, and the refractive nonlinearities of S-1, S-1＇, and T-1. The close match between the theory and experiment not only shows the completeness of the five-level kinetic model but also demonstrates the close relationship between the optical nonlinearities of HA and the dynamics involved in excited-state intramolecular proton transfer.