The purpose of this study was to determine the effects of an acute oral dose of 3 mg·kg(-1) of Rhodiola rosea on endurance exercise performance, perceived exertion, mood, and cognitive function. Subjects (n = 18) ingested either R. rosea or a carbohydrate placebo 1 hour before testing in a double-blind, random crossover manner. Exercise testing consisted of a standardized 10-minute warm-up followed by a 6-mile time trial (TT) on a bicycle ergometer. Rating of perceived exertion (RPE) was measured every 5 minutes during the TT using a 10-point Borg scale. Blood lactate concentration, salivary cortisol, and salivary alpha amylase were measured before warm-up, 2 minutes after warm-up, and 2 minutes after TT (n = 15). A Profile of Mood States questionnaire and a Stroop Color Test were completed before warm-up and after TT. Testing was repeated 2-7 days later with the other condition. Rhodiola rosea ingestion significantly decreased heart rate during the standardized warm-up (R. rosea = 136 ± 17 b·min(-1); placebo = 140 ± 17 b·min(-1); mean ± SD; p = 0.001). Subjects completed the TT significantly faster after R. rosea ingestion (R. rosea = 25.4 ± 2.7 minutes; placebo = 25.8 ± 3.0 minutes; p = 0.037). The mean RPE was lower in the R. rosea trial (R. rosea = 6.0 ± 0.9; placebo = 6.6 ± 1.0; p = 0.04). This difference was even more pronounced when a ratio of the RPE relative to the workload was calculated (R. rosea = 0.048 ± 0.01; placebo = 0.057 ± 0.02; p = 0.007). No other statistically significant differences were observed. Acute R. rosea ingestion decreases heart rate response to submaximal exercise and appears to improve endurance exercise performance by decreasing the perception of effort.