The aim of this study was to investigate the effects of guarana supplementation on cognitive performance before and after a bout of maximal intensity cycling, and to compare this to an equivalent caffeine dose. Twenty-five participants completed the randomised double-blind crossover trial by performing cognitive tests with 1 of 3 supplements, on 3 different days: guarana (125 mg/kg), caffeine (5 mg/kg) or placebo (65 mg/kg protein powder). After 30-minutes of rest, participants performed simple (SRT) and choice reaction time (CRT) tests, an immediate word recall test and Bond-Lader mood scale. This was followed by a cycling V̇O2max test, cognitive tests were then immediately repeated. Guarana supplementation decreased CRT before exercise (407 ± 45ms) in comparison to placebo (421 ± 46ms, P=.030) but not caffeine (417 ± 42ms). SRT after exercise decreased following guarana supplementation (306 ± 28ms) in comparison to placebo (323 ± 32ms, P=.003) but not caffeine (315 ± 32ms). Intraindividual variability on CRT significantly improved from before (111.4 ± 60.5ms) to after exercise (81.85 ± 43.1ms) following guarana supplementation, no differences were observed for caffeine and placebo (P>.05). Alertness scores significantly improved following guarana supplementation (63.3 ± 13.8) in comparison to placebo (57.4 ± 13.4, P=.014) but not caffeine (61.2 ± 12.8). There were no changes to V̇O2max, immediate word recall or any other Bond-Lader mood scales. Guarana supplementation appears to impact several parameters of cognition. These results support the use of guarana supplementation to possibly maintain speed of attention immediately following a maximal intensity exercise test (V̇O2max).