Purpose: To investigate brain oscillatory patterns underlying prolonged attentional performance as a function of cardiorespiratory fitness in healthy young adults. Design: Cross-sectional study. Method: Two groups of participants (25 higher-fit and 25 lower-fit) were compared in terms of reaction time (RT) performance, tonic electroencephalographic (EEG) overall dynamics, and event-related spectral perturbation (ERSP) in a 60’ version of the psychomotor vigilance task. Resting state EEG was also measured. A submaximal cardiorespiratory fitness test confirmed the between-groups difference in terms of aerobic fitness. Results: Descriptive behavioural data showed shorter RTs in higher-fit participants, but only during the first 30’ of the task. Crucially, this same period was accompanied by increased theta (4-8 Hz) and upper beta (20-40 Hz) power and reduced alpha (8-14 Hz) and lower beta (14-20 Hz) suppression after the target stimulus presentation compared to their lower-fit peers, but these differences disappeared in the second part of the task. Additionally, lower-fit showed greater suppression of upper beta power than higher-fit after the cue stimulus presentation, an effect that was not modulated by the time-on-task. EEG overall dynamics results did not show significant differences between groups, although they also evidenced interesting differential brain oscillatory patterns as a function of aerobic fitness both at rest and during task performance. Conclusions: Cardiorespiratory fitness was related to a brain oscillatory differential response pattern over a wide range of the frequency spectrum and spatio-temporal distribution, which seems to underlie the positive association between aerobic fitness and sustained attention.