This study aims to investigate the predictive roles of rumination, mindfulness and demographic variables on positive and negative affect of university students. The study was designed as a predictive correlational research model. The data were collected from 466 students through the Positive and Negative Affect Schedule, the Ruminative Thought Style Questionnaire, the Philadelphia Mindfulness Scale, and a demographic questionnaire and analyzed with multiple linear regression analysis. According to the results, rumination, mindfulness (awareness and acceptance), age, gender, and romantic relationship status as a whole accounted for 15% of the variance in positive affect and explained 28% of the variance in negative affect. Positive affect was predicted by awareness and age positively and by acceptance and rumination negatively; negative affect was predicted by rumination and romantic relationship status positively and by acceptance negatively. Being female led to a decrease in positive affect. Implications to the education and counseling field were discussed.