Structural relaxation and viscosity of As2S3 glass were studied by length dilatometry. The Tool-Narayanaswamy-Moynihan model was successfully applied for the quantitative description of isothermal and isochronal experiments performed within 40 degrees C below T-g. The activation energy of relaxation process is identical within the experimental errors with that of viscous flow which was found to be 267 kJ/mol. The non-linearity and non-exponentiality parameters were evaluated as x=0.31 and beta=0.82, respectively.