The effects of Houttuynia cordata powder on the growth performance of ducks were investigated. Ninety ducks were assigned into one of three dietary treatments as a completely randomized design for 6 weeks: feeds supplemented with 1% or 2% H. cordata and a control group. No significant difference was observed in feed conversion among the three groups (p > 0.05), but addition of H. cordata had a significantly positive effect (p < 0.05) on initial and final body weight, weight gain, and feed intake of the ducks. Furthermore, the effects of chemical treatment (comprising 50 g and 100 g aluminum chloride [AlCl3] per kilogram litter) on the ammonia (NH3) flux in duck litters were also investigated. Duck litter was treated with AlCl3 at a depth of 8 cm by top-dressing; this resulted in a significant difference on NH3 flux (p < 0.05) during the experimental period (but not at 2 weeks). NH3 flux at 6 weeks were reduced by 25.4% and 37.5% by treatment with 1% and 2% H. cordata, respectively, compared with the control groups. In conclusion, enriching the diets of the ducks with 2% H. cordata and adding 100 g AlCl3 to their litter has beneficial effects on increasing their growth performance and reducing NH3 flux in their environment.