Using a Ar + laser at 458 nm or a ps-Nd : YAG laser at 355 and 532 nm, a broad photoluminescence peaked at 530 nm from a barium titanate (BTO) crystal was observed. The lifetime was measured to be 10 ns at room temperature. In a time-resolved degenerate-four-wave-mixing (DFWM) measurement the fast nonlinear optical response was found to be strongly orientation dependent. With grating vector perpendicular to C-axis, only a narrow response signal with the half-width of 30 ps was observed while in a parallel configuration the response signal was hundred times broader, showing an exponential decay with the rate of 1.8–2.5 × 108 s. A proposed theoretical model suggests that the charge carriers produced in the conduction band may be trapped at Ti 4+ center to form Ti 3+ , causing a temporary lattice distortion along the direction of the internal poling electric field which changes polarizability.