Two experiments explore the effects of mood on category learning. In the first experiment subjects were put into either a negative or a neutral mood before completing one of two category-learning tasks. Negative mood briefly impaired rule-based category learning but this impairment did not persist throughout the task. Negative mood did not influence non-rule-based learning. In a second study subjects learned one of three category sets (easy rule-based, hard rule-based, non-rule-based) by Shepard, Hovland & Jenkins (1961) and completed the Beck Depression Inventory (BDI-II). A significant negative correlation was found between hard rule-based performance and subject scores on the BDI-II. No significant correlations were found between subject scores on the BDI-II and easy rule-based or non-rule-based performance. These results suggest that negative affect does not significantly impair category learning but the absence of positive affect (as measured by the BDI-II) is negatively related to complex rule use.