A cuprous oxide particle dispersion liquid includes: cuprous oxide particles; 20 to 100 parts by mass of a phosphate ester-based anionic surfactant per 100 parts by mass of the cuprous oxide particles; and 500 to 10000 parts by mass of an organic solvent per 100 parts by mass of the cuprous oxide particles. The cuprous oxide particles have an average primary particle diameter of 2 nm to 80 nm and have an average secondary particle diameter of 50 nm to 150 nm, the average secondary particle diameter being measured by dynamic light scattering using cumulant analysis. A coating agent composition includes the cuprous oxide particle dispersion liquid and a binder resin, wherein the cuprous oxide particles are contained in a range from 0.1 to 50 parts by mass in 100 parts by mass of a non-volatile matter content of the coating agent composition. An antibacterial/antiviral member includes a substrate and a coating film formed on the substrate and containing the coating agent composition.