Al2O3-coated cordierite has been widely used as a catalyst's support. In this work, three Al2O3 precursors or alumina sots are studied to understand the effect of type, viscosity, and grain size of the sots and Cl- on properties and SCR activities of honeycomb CuO/Al2O3/cordierite catalysts. X-ray diffraction (XRD), N-2 adsorption, scanning electron microscopy and energy dispersive X-ray (SEM-EDX) techniques are used for analyses. Results show that the viscosity and average grain size of the sol have significant influences on the amount and stability of the Al2O3 coating. The sol synthesized from AlCl3 and aluminum is the best among the three sots in terms of less coating cycle, stability of the coating, and selective catalytic reduction (SCR) activity. Cl1- introduced in preparation must be washed out because it deactivates the SCR activity.