This study investigates the effect of grain boundary sliding (GBS) and material properties on the extrusion of through-silicon via. A finite element model is set up to evaluate via extrusion during thermal cycling taking into account the actual grain structures near the via top. The elastic anisotropy and plasticity are considered for each Cu grain, and the grain orientation obtained from experimental measurements is directly mapped into the FEA model. GBS is described by a cohesive zone model based on a frictional traction separation relationship. Based on GBS, the via extrusion behavior is deduced for two different Cu/Si interfacial conditions: fully bonded and free sliding, corresponding to the upper and lower bounds of the extrusion. In each case, the effect of GBS is evaluated by analyzing the plasticity and extrusion profiles. The results indicate that GBS plays a dominant role in determining the magnitude and profile of via extrusion.