Although electroless copper deposition has been widely used in the electronic industry, the selection of the bath solutions relies still on some empirical rules. This paper provides a further exploration of the bath compositions for electroless copper plating. It was found that the formation of Cu2O in electroless copper plating is associated with the presence of Cu(OH)(2) in the bath. A chemical equilibrium calculation was thus made for the avoidance of Cu(OH)(2) in an electroless copper bath. Sodium thiosulfate was found to be an effective stabilizer for electroless copper plating. The plating was further optimized based on a statistical design of sorts, namely, Taguchi’s approach. Effects of individual components on the plating rate were discussed.