Exploration is an important part of decision making and is crucial to maximizing long-term reward. Past work has shown that people use different forms of uncertainty to guide exploration. In this study, we investigate the role of the pupil-linked arousal system in uncertainty-guided exploration. We measured participants’ pupil dilation (N = 48) while they performed a two- armed bandit task. Consistent with previous work, we found that people adopted a hybrid of directed, random and undirected exploration, which are sensitive to relative uncertainty, total uncertainty and value difference between options, respectively. We also found a positive correlation between pupil size and total uncertainty. Furthermore, augmenting the choice model with subject-specific total uncertainty estimates decoded from the pupil size improved predictions of held-out choices, suggesting that people used the uncertainty estimate encoded in pupil size to decide which option to explore Together, the data shed light on the computations underlying uncertainty-driven exploration. Under the assumption that pupil size reflects Locus Coeruleus-Norepinephrine (LC-NE) neuromodulatory activity, these results also extend the theory of LC-NE function in exploration, highlighting its selective role in driving uncertainty- guided random exploration.