Summary Relaxation behavior of GeySe100-y (y=8 and 10) glasses related to the viscosity behavior was studied by dilatometry. The method of two consecutive temperature jumps was applied to study the volume relaxation. The relaxation response can be described by Tool-Narayanaswamy-Moynihan model and the parameters of this model ?h*, ß, x, A were determined using curve fitting method and characteristic times method. Viscosities of studied materials in the range of 108-1013 Pas were measured by penetration method. The calculated values of activation energies of viscous flow E? are close to the values of effective activation energies of relaxation ?h* for studied chalcogenide materials.