Strengthening of electrodeposited Au-based materials is achieved by co-electrodeposition with TiO2 nanoparticles dispersed in a sulfide-based gold electrolyte. TiO2 content in the composite film is adjusted by concentration of the TiO2 in the gold electrolyte. Effects of the TiO2 content on surface morphology, crystalline structure and microstructure of the composite film are investigated. Mechanical properties of the Au–TiO2 composite films are evaluated by micro-Vickers hardness and micro-compression tests. The hardness increases from 135 to 207 HV when the TiO2 content is increased from 0 to 2.72 wt%. Specimens used in the micro-compression test are micro-pillars fabricated from the composite film, and the yield strength reaches 0.84 GPa by incorporating 2.72 wt% TiO2 into the film.