The non-resonant third-order non-linear optical properties of some amorphous chalcogenide films were studied experimentally by the method of the femtosecond optical heterodyne detection of the optical Kerr effect. The real and imaginary parts of the complex thirdorder optical non-linearity could be effectively separated and their values and signs could be also determined. Amorphous chalcogenide films showed a very fast response in the range of 200 fs under ultrafast excitation. The ultrafast response and large third-order non-linearity are attributed to the ultrafast distortion of the electron orbitals surrounding the average positions of the nucleus of chalcogen atoms. The high third-order susceptibility and a fast response time of amorphous chalcogenide films make them promising materials for application in advanced techniques especially in optical switching.