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Micron-size Ni-base alloy (NBA) powders were mixed with both 1.5 wt.% (hereinafter %) micron-size CeO 2 (m-CeO 2 ) and also 1.5% and 3.0% nano-size CeO 2 (n-CeO 2 ) powders. These mixtures were coated on low-carbon steel (Q235) by 2.0 kW CO 2 laser cladding. The effects on the microstructures, phases and electrochemical corrosion of the coatings upon the addition of m-and n-CeO 2 powders to NBA (m-and n-CeO 2 /NBA) have been investigated. The results showed that a smooth coating was prepared under suitable processing parameters (P = 2.0 kW, V = 180 mm min −1 ) by adding 1.5% n-CeO 2 . In addition to the primary phases of γ -Ni, Cr 23 C 6 and Ni 3 B in the Ni-base alloy coating, CeNi 3 was formed in Ni-base alloy coatings with both n-CeO 2 and m-CeO 2 particles, and CeNi 5 appeared in the coating upon decreasing the size of CeO 2 particles. Well-developed dendrites were observed in the Ni-base alloy coating; directional dendrites grew at the interface in the coating upon the addition of m-CeO 2 , whereas fine and multioriented dendrites grew upon decreasing the size of CeO 2 particles to the nanoscale. Actinomorphic dendrites and compact equiaxed dendrites grew from the interface to near the surface upon increasing the content of n-CeO 2 from 1.5 to 3.0%. In strongly acidic HNO 3 solution, the severe corrosion of dendrites occurred and there were many corrosion pits in the Ni-base alloy coating; intercrystalline corrosion also has a dominant role upon the addition of m-CeO 2 , whereas uniform corrosion occurs in the coating as the size of CeO 2 particles is decreased to nanoscale.