The rise in the use of opioids has been accompanied by increases in prescription opioid misuse among patients with chronic pain. Opioid craving has emerged as a robust determinant of opioid misuse, but the factors that contribute to opioid craving have yet to be fully elucidated. Perceived injustice has been linked to numerous negative pain outcomes, but little is known about its association with opioid craving. Objectives: The first objective of this study was to examine the association between perceived injustice and opioid craving in patients with chronic pain who are prescribed opioids. We also examined whether pain intensity, negative affect, or catastrophizing mediated this association. Methods: In this longitudinal diary study, patients (n = 103) completed a questionnaire assessing perceived injustice and then completed daily measures of pain intensity, negative affect, catastrophizing, and opioid craving for 14 consecutive days. Results: A significant association was found between perceived injustice and opioid craving (P < 0.01), with higher levels of perceived injustice being associated with heightened levels of opioid craving. A 2-1-1 multilevel mediation analysis indicated that the association between perceived injustice and craving was significantly mediated by catastrophizing (P < 0.05). Conclusions:The present study provides new insights into the factors that might contribute to opioid craving in patients with chronic pain. Our findings suggest that perceived injustice might lead to increased catastrophizing and, in turn, heightened daily levels of opioid craving. These findings could have implications for chronic pain management clinicians who prescribe opioids.