The intrinsic brittleness and ductility of intergranular cracks in Cu bicrystals under quasi-static loading conditions are investigated using molecular statics simulations. Central cracks are inserted into nine I 11 pound tilt grain boundaries with different inclination angles, seven of which are asymmetric, and two of which are symmetric. On the basis of results of molecular statics simulations, critical energy release rates at material failure are calculated using the corresponding continuum counterparts with the finite element method. Simulation results are compared to predictions made on the basis of Rice's model, and the applicable range of Rice's model is given in terms of inclination angle. The effects of inclination angle on the mechanical properties of grain boundaries and fracture mechanisms of the corresponding intergranular cracks are analyzed in detail.