The effects of energy-saving hydraulic fluids are confirmed by not only many actual hydraulic systems but also bench tests using hydraulic pump. We have studied some laboratory evaluation methods that are simpler than bench test using hydraulic pump. In this paper, we report some results of roller on disk test, which reflects the tribological condition of a piston pump. Specimen Roller was made from metals used for the piston of a piston pump, and specimen disks were made from seven different metals used for the cylinder block of a piston pump. The evaluation condition of hydraulic fluid by the roller on disk test was established. In this condition, the widely used anti-wear fluid has higher friction coefficient than energy saving type, and in energy saving type, the friction coefficients become lower with time in all metal combinations. It agrees very well with the energy-saving effect of hydraulic fluids in an actual hydraulic system.