Background: To examine the effect of acute Rhodiola Rosea (R.Rosea) ingestion, acute caffeine ingestion, or combined caffeine and R.Rosea on 5-km running time trial performance. Methods: Twelve male recreational exercisers (mean age ± SD: 24.6 ± 6 years) undertook four trials each (placebo, caffeine [3 mg.kg−1], R.Rosea [3 mg.kg−1], and caffeine [3 mg.kg−1] and R.Rosea [3 mg.kg−1]) in a double-blind randomized order. Results: There was a small but significant main effect of treatment for 5-km run time (p = 0.048) where performance was faster in the presence of caffeine compared with placebo, but not between any other combination of trials. Heart rate, blood lactate, and rating of perceived exertion increased with km run, irrespective of substance ingested (all p < 0.05). Scores for Felt Arousal increased preingestion to postingestion (p = 0.028) and were maintained to postexercise (p = 0.026), irrespective of the substance ingested. There was a small significant treatment × time interaction (p = 0.011, Pη...