We evaluated meat quality and color of breast during storage in ducks fed diet supplemented with different forms of Houttuynia cordata (HC) with fermented red koji (FRK). In total, 240 one-day-old Pekin ducks (160 males and 80 females) were allocated to four diet treatments (control, 1% HC powder mixed with FRK, pelleted 1% HC with FRK, and coated pellets of 1% HC with FRK). At days 3 and 7 of storage, pH values were slightly influenced (p < 0.05) by different forms of HC with FRK, but was no influence at day 0 of storage day. Diet treatments with different forms of HC and FRK had an effect (p < 0.05) on TBARS values at 0, 3, and 7 days of storage and DPPH radical-scavenging activity at 0 days of storage, except for cooking loss. Overall, in breast meat of ducks, L* values at day 3 of storage and a* values at day 0 of storage were significantly influenced (p < 0.05) by treatments with different forms of HC and FRK. In conclusion, using either 1% HC and FRK pellets or pellets coated with HC and FRK at 1% resulted in a decrease in TBARS values and an increase in DPPH radical-scavenging activity during storage.