Retinal derivatives were synthesized and their third‐order nonlinear optical properties were measured by degenerate four‐wave mixing with temporally incoherent nanosecond laser pulses. Fast optical nonlinearities, whose response time was shorter than 30 ps, were observed. The magnitudes of resonant third‐order hyperpolarizability were found to be 10−31∼10−29esu. The large optical nonlinearities were of electronic origin.