Design/methodology/approach The lubricating oils containing sulfur-based additives of T563 and T561 at concentrations of 0.5 Wt.%, 1 Wt.%, 1.5 Wt.% and 2 Wt.% were prepared. The tribological performance was evaluated under boundary lubrication condition. In addition, the T561 concentration affects the tribological performance under mixed lubrication condition was extensively studied. Findings Under boundary lubrication condition, the wear rates of copper alloy lubricated by T561 were significantly lower than those lubricated by T563 at the same concentrations. At 1 Wt.% concentration, the wear rates of copper alloy lubricated by T561 was 1.32 × 10–6 mm3/N·m, representing a 65% reduction in comparison with T563. The optimal lubrication performance was achieved with 1 Wt.% T561 under mixed lubrication condition, where the average friction coefficient and wear rates were recorded at 0.068 and 0.3 × 10–6 mm3/N·m, respectively, demonstrating reductions of 15% and 60% compared to the base oil. Through EDS and XPS analyses, physical adsorption and tribo-chemical reactions were occurred for T561 on the copper alloy, resulting in the formation of a protective film primarily composed of CuS. Originality/value The incorporation of T561 has been demonstrated to effectively enhance the wear resistance of copper alloys when lubricated by hydraulic oil. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2025-0083/