The optical properties of Ge-Sb-Se glasses have been extensively studied at telecom wavelengths in recent years. However, the understanding of nonlinearity in Ge-Sb-Se glasses at mid-infrared wavelengths still remains limited. In this work, a series of Ge20SbxSe80-x (x=0, 5, 10) glasses were prepared by conventional melt-quenching method. The absorption spectra and the refractive index of glasses were recorded. The third order nonlinearity, n(2), and nonlinear absorption coefficient were measured for Ge-Sb-Se glass samples at the wavelengths of 1550, 2000 and 2500 nm by Z-scan technique, respectively. With the increasing of Sb contents, the linear refractive index of glass increased. Among the three operating wavelengths, all the three glass samples have a highest n(2) at 2000 nm. By using the figure of merit (FOM) to evaluate the studied three glasses, the Ge20Sb10Se70 glass shows the greatest potential for mid-IR all optical switching devices. (C) 2015 Elsevier Ltd. All rights reserved.