In this work, the Co-doped ZnO rods were prepared by the hydrothermal method. The size of these rods can be changed from micro-size to nano-size by using different solutions during the preparation. The results of transmission electron microscopy (TEM) and selected area electron diffraction (SAED) showed that the as-prepared nano-sized Co-doped rods have single-crystal structure. The polarized Raman experiments were presented on an individual micro-sized Co-doped ZnO rod in the $X(YY)vec{X}$, $X(ZY)vec{X}$ and $X(ZZ)vec{X}$ configurations, the results of polarized Raman indicated that these rods are crystallized and their growth direction is parallel to c-axis.