The purpose of this research is to examine the effects of tennis players' life engagement and positive thinking skills on mental thoughness in university teams and to reveal them in terms of some demographic variables (age, gender, being a national athlete, duration of playing tennis, tournament categories participated and dominant hand).

The sample group of this research consisted of 200 athletes (108 men, 92 women) who participated in Turkey Unilig tennis competitions held in Antalya in 2017 and were surveyed on a voluntary basis. Three scales were used as data collection tools in the survey. First scale; The Life Engagement Scale developed by Scheier et al. and adapted to Turkish providing validity and reliability by Uğur and Akın. Second scale; Positive Thinking Skills Scale developed by Bekhet and Zauszniewski and adapted to Turkish providing validity and reliability by Akın et al. As the third scale; The Short Psychological Endurance Scale developed by Smith et al. and adapted to Turkish providing validity and reliability by Akın et al.

In the analysis of the data used in this research; t-test, one-way analysis of variance (ANOVA) and correlation analyzes were used. Since the data have normal distribution, the "Anova-Homogenety of variance" test was applied to determine homogeneity by the single sample "Kolmogorov-Smirnov" test and parametric data were found to have homogeneous and normal distribution.

According to the findings obtained after the statistical evaluation, a significant moderate positive relationship was found between the psychological endurance and the positive thinking relationship of tennis players participating in the survey. There was a statistically insignificant but positive and small association between life engagements and psychological endurance. It was also found that there is an insignificant positive and weak relationship between life engagement and positive thinking.

There was no significant difference between the averages of psychological endurance and gender, duration of playing tennis, gender, national athlete, age, dominant hand  and tournament category participated.