Previous research has shown that rumination is negatively correlated with forgiveness across a wide range of relationships. In addition, experimental research has revealed that rumination increases anger and aggressive retaliatory behavior following an interpersonal offense. The current study was designed to expand upon these findings by providing an experimental investigation of rumination, anger, and forgiveness in the context of marital relationships. We sought to determine whether rumination had a causal effect on anger, forgiveness, explicit attitudes, and implicit attitudes toward one's spouse. Spouses were randomly assigned to either ruminate or engage in cognitive reappraisal of a transgression they had recently experienced in their marriage. Following this thought manipulation task, we assessed subjects' anger, forgiveness, explicit attitudes, and implicit attitudes toward their spouse. The results revealed that rumination led to an increase in subjects' anger toward their spouse from pre- to post-manipulation, while cognitive reappraisal did not cause any changes in subjects' anger. After controlling for baseline rumination, we found that rumination led to lower motivations for forgiveness than cognitive reappraisal. In addition, anger mediated the effect of rumination on forgiveness. Contrary to our predictions, rumination and cognitive reappraisal did not cause differences in subjects' negative explicit or implicit attitudes toward their spouse. We conclude that the relationship between rumination and forgiveness may be causal and not simply correlational, and that anger seems to play a significant role by mediating this effect.