The main purpose of this present research is to contribute to the understanding of time-dependent behavior of homogeneous, isotropic hard rocks. Chapter I deals with the study of different parameters which influence rock behavior : existing microstructures of the Lattice water content temperature deformation mechanisms change of homogeneous to brittle behaviour (deformation localization) scale effects, experimental setup, different test types Chapter II deals with rheology, its theoretical, basis, principles and recent developments : need of an incremental formulation of the behavior laws in the lattice review of the incremental formulation of elastoplastic laws extension of the incremental formulation to time-dependent laws classification of time-dependent laws viscous behaviour of rocks Chapter III is, above all, experimental. It then proposes how to determine a rheological model by taking into account the uniaxial test results, that is : quasi static tests, at constant rate time dependent tests : creep tests during 15 days or less some relaxation tests, ranging from a few minutes to half an hour