The purpose of this study was to examine whether the leisure involvement of adults who participate in fitness activities has an effect on positive and negative affect. The relational screening model, one of the quantitative research methods, was used. In this study, the “Leisure Involvement Scale” and the “Positive and Negative Affect State Scale” were used. Descriptive statistics, parametric tests such as Pearson's correlation test and simple regression analysis were used to analyses the data. In addition, validity and reliability analyses were carried out to determine the validity and reliability coefficients of the scales. It was found that leisure involvement and its sub-dimensions have an effect on positive and negative affect states. As a result, it was concluded that positive emotional states increased, and negative emotional states decreased in adult individuals who participated in leisure-time fitness exercise. Therefore, it shows that it can help adults cope with the negative emotions they encounter in their daily lives (stress, anxiety, burnout, depression, lack of self-esteem, social appearance anxiety, etc.).