Nanoparticulate platinum (II) (nano Pt) is a powerful antioxidant that is widely used to scavenge reactive oxygen species (ROS). The antioxidant activity of nano Pt has gained attention as a potentially useful therapeutic for a variety of diseases including cancer and aging. In the present study, we prepared nanoparticulate saponin-Pt (II) (nano saponin-Pt) conjugates using the ethanol reduction method to enhance the permeability and retention effect of Pt. The nano saponin-Pt conjugates were found to restore the viability of approximately 40% of 2,4-dinitrofluorobenzene (DNFB)-treated RAW 264.7 cells. In addition, we found that nano saponin-Pt conjugates acted as a potent antioxidant that reduced the production of ROS and inhibited activation of the MAP kinase pathway and MIP-2 gene expression in response to DNFB. These results provide insight into the potential usefulness of nano saponin-Pt conjugates as a treatment for contact hypersensitivity.