Ag nanoparticles have been fabricated on the surface of CMK-3 mesoporous carbon through an immersion-electrodeposition (IE) technique. Transmission electron microscopy analysis indicated that it was a facile approach to electrochemically prepare nano-sized Ag clusters. Electrochemical experiments showed that Ag nanoproducts were efficient electrocatalysts for anodic oxidation of formaldehyde in alkaline solutions, and as the reduced of the potential value, the electrocatalytic peak current density for the formaldehyde electro-oxidation reaction was increased gradually. Also, the electrocatalytic activity of Ag/CMK-3 nanocatalysts for formaldehyde electro-oxidation is higher than that of Ag/XC-72 nanocatalysts. These findings represented a significant step toward the implementation of individual Ag/CMK-3 nanocatalysts as anodic materials in fuel cells and sensors.