Electrodeposited Al₂O₃ composite Cr-C alloy coatings were produced from an oxalic acid bath prepared by adding oxalic acid to a hot CrO₃ solution. Chromium ions in the oxalic bath include Cr^3＋ oxalate complex and Cr^6＋ ions. The Al₂O₃ particles were co-deposited easily along with the Cr-C alloy coating from the oxalic bath. The content was controlled up to about 3 wt% by plating conditions. The Al₂O₃ contents of the coatings decreased with current density and increased with bath temperature. The added amount of oxalic acid at make-up of the bath increased the Al₂O₃ contents of the coatings. The co-deposition mechanism was supported with a two-step adsorption mechanism proposed by Guglielmi, but the adsorption of Al₂O₃ tothe cathode in the oxalic bath was much weaker than that of either Ni composite plating or Cr composite plating.