Fluralaner is a novel drug belonging to the isoxazoline class that acts on external parasites of domestic animals. It is used systemically via drinking water, especially against red poultry mite in layer chickens. Fluralaner is frequently used in layers infected with D. gallinae. However, no study to date has investigated the effects of feed intake and water hardness.This study aimed to investigate the effects of variable water hardness and feed intake on the pharmacokinetic profile of fluralaner.Layer chickens were divided into four groups (n = 8): fed + purified water (Group 1), feed restricted + purified water (Group 2), feed restricted + hard water (Group 3), and feed restricted + soft water (Group 4). After administering a single dose of the drug with drinking water, the blood samples were collected for 21 days. Fluralaner concentrations in plasma samples were determined by liquid chromatography/tandem mass spectrometry. The maximum plasma concentration (Cmax), time to reach maximum plasma concentration (tmax), area under the concentration-time curve values (AUC0-21d), half-life (t1/2), and other pharmacokinetic parameters were calculated.Although the highest maximum plasma concentration (Cmax) was determined in Group 1 (fed + purified water), no statistically significant difference was found in the Cmax, tmax, t1/2, MRT0-inf_obs, Vz/Fobs, and Cl/F_obs parameters between the experimental groups.It was concluded that the feed intake or water hardness did not change the pharmacokinetic profile of fluralaner in layer chickens. Therefore, fluralaner could be used before or after feeding with the varying water hardness in poultry industry.