Effect of Tl on the electrodeposition behavior of Au was investigated by electrochemical analysis, total-reflection X-ray fluorescene analysis, XRD, glow discharge optical emission spectrometer (GD-OES) and hardness measurement. The deposition rate increased with an increase in the amount of Tl addition to the bath. Tl was co-deposited at the interface between the seed layer and the Au films, as well as in the films. In asdeposited condition, the Tl contained films exhibited higher hardness compared with the Tl-free films, while both of them showed almost the same hardness after annealing. It was suggested that the hardness is correlated with the crystal orientation of the grains.