Emotion dynamics, how people’s emotions fluctuate across time, represent a key source of information about people’s psychological functioning and well-being. Investigating emotion dynamics in the workplace is particularly relevant, as affective experiences are intimately connected to organizational behavior and effectiveness. In this study, we examined the moderating role of emotional inertia in the dynamic association between both positive and negative emotions and self-rated job performance among a sample of 120 Italian workers (average age 41.4, SD = 14), which were prompted six times per day, for five working days. Emotional inertia refers to the extent that emotional states are self-predictive or carry on over time and is measured in terms of the autocorrelation of emotional states across time. Although inertia has been linked to several indicators of maladjustment, little is known about its correlates in terms of organizational behavior. Findings revealed that workers reporting high levels of positive emotions and high inertia rated their performance lower than workers high in positive emotions, but low in inertia. In contrast, the relation between negative emotions and performance was not significant for either high levels of inertia or low levels of inertia. Taken together, these results suggest the relevance of investigating the temporal dependency of emotional states at work.