20-nm-thick (CoPt)_100-xAg_x and (CoPd)_100-xAg_x (001) films (x = 0-20) were grown on MgO(001) substrate at a temperature of 300°C by molecular beam epitaxy, and their crystal structure and magnetic properties were compared with those of FePt-Ag and FePd-Ag films [Y. Tokuoka et al.: J. Appl. Phys., 115, 17B716 (2014)] for the systematic study of the effect of Ag addition into transition metal - noble metal alloy films. For the CoPt-Ag, the addition of 5% Ag increased perpendicular magnetic anisotropy (PMA) and coercivity. However, for the CoPd-Ag, Ag addition enhanced neither the PMA nor the coercivity. Structural analysis of the CoPt-Ag and CoPd-Ag films revealed that Ag addition promoted L1₀ phase ordering for CoPt-Ag, while L1₀ ordering was not found in CoPd-Ag. Although there were some similarities in the effect of Ag addition between CoPt-Ag and FePt-Ag, such as increased PMA, coercivity, and L1₀ ordering, there were different trends in PMA and L1₀ ordering between CoPd-Ag and FePd-Ag, except that both films showed reduced coercivity with Ag addition. Ag segregation and L1₀ ordering are considered important factors to explain the variations of structure and magnetic properties with Ag addition.