One hundred and twenty Cihateup ducks in the grower phase aged 14 weeks with an average body weight of 1049.8±48.61 g, from the Poultry Livestock Laboratory, Faculty of Animal Science, Padjadjaran University, were used in this study to determine the effectiveness of flavonoids (FLA) in preventing ileum plaque-patch (PP) damage in heat-stressed Cihateup duck. Animal samples were given four treatments with six replications, the number of each replication was five Cihateup ducks. The study was conducted with five types of experimental treatment, as follows: F1: Without heat stress (HS) (25 °C) and without FLA; F2: HS (39 °C) with 50 mL FLA/sample; F3: HS (39 °C) with 750 mL FLA/sample; F3: HS (39 °C) with 100 mL FLA/sample. Administration of FLA was carried out every morning before being given drinking water and rations, by means of orally. Each cage was equipped with an incandescent lamp as a heat source and a thermostat, with a temperature range of 38–40 °C or an average of 39 °C. Heat treatment was exposed from 06.00 a.m. to 08.00 p.m. Staining methods by Acid Mallory were used in this study to identify and measure plaque-patch (PP) metrics. Based on the results of this study, it was shown that the administration of FLA at a dose of 75 mL was able to prevent ileum plaque-patch damage in heat-stressed Cihateup ducks. [ABSTRACT FROM AUTHOR]