Background and Aims. Caffeine mouth rinsing has emerged as an alternative to oral caffeine consumption for improving performance without provoking lower gastrointestinal distress. However, it remains unclear if hydration status and sweat rate are negatively affected by caffeine mouth rinsing. This study is aimed at evaluating the effects of 10 seconds of caffeine mouth rinsing (1.2% anhydrous caffeine solution) on hydration status and sweat rate following a 10 km run trial. Methods. Ten recreationally trained runners () volunteered to participate in this double-blind, placebo-controlled, and crossover research study. Participants completed two 10 km run trials separated by approximately one week. Immediately prior to running, participants completed a 10-second mouth rinse protocol with either 300 mg of caffeine or microcrystalline cellulose (placebo) diluted in 25 mL of water. The effects of caffeine mouth rinsing on hydration status and sweat rate were assessed following a 10 km run trial. Results. Sweat rate (placebo: vs. caffeine: ; ), dehydration (placebo: vs. caffeine: ; ), and hydration (placebo: vs. caffeine: ; ) measures were not significantly different between trials. Conclusion. Caffeine mouth rinse does not appear to alter the hydration status or sweat rate following a 10 km run.