Yttria stabilized zirconia (Y-CSZ) single crystals show plastic deformation at high temperatures byactivating dislocations. The effect of strain rate on the plastic behavior of this crystal was studied. As increasingstrain rate from ε=1.04×10-5sec-1 to 2.08×10-5sec-1 the yield drop was suppressed and resulted in higherYoung's modulus and yield stress. Dislocation structures of the strained crystals were analyzed using atransmission electron microscope to elucidate the plastic behavior of these crystals. In the early stage of plasticdeformation, dislocation dipoles and prismatic dislocation loops were formed in both samples. However,dislocation density was increased by increasing strain rate. Strong sessile dislocations were observed in thesample with higher strain rate, which may cause the higher work hardening.