An ambient temperature glyoxylic acid Cu-L-（＋）-potassium sodium tartrate system was evaluated as a formaldehyde-free electroless copper plating bath for applying thin conductive coatings in through-holes of printed circuit boards. Electrochemical behavior and plating tests demonstrated that the copper concentration, not the glyoxylic acid concentration, should be controlled appropriately to deposit copper. The copper concentration should be less than 0.03 mol･dm⁻³. Neither increasing the catalyst concentration nor raising the temperature during catalyst adsorption to increase catalyst adsorption within the through holes improves the plating coverage within the through-holes. Adding sodium metasilicate, bipyridyl or polyethylene glycol alone does not improve the plating coverage in the through holes. However, co-addition of sodium metasilicate or bipyridyl together with polyethylene glycol can improve plating uniformity in the through-holes. Nevertheless, effective plating is only achieved at approximately pH 12.7. The glyoxylic acid concentration was remarkably low in that pH region because of the Cannizzaro reaction. Future challenges for this system using L-（＋）-potassium sodium tartrate as a complexing agent are the achievement of high GOA retention and uniform plating in the through-holes.