The current study aimed to identify the relationship between optimism and psychological immunity. It also aimed to reveal the dimensions of optimism predicting the psychological immunity among university students. The sample consisted of (411) university students (100 males – 311 females) in the first year of theoretical and practical colleges aged between (18 – 19) years old with average age (18.72) years with standard deviation (0.64) year. The optimism scale (prepared by: the researcher 2020) and the psychological immunity scale (prepared by: Esam Zydan 2013) were applied. The results concluded that: there is a statistically significant positive correlation between the university students' scores on the optimism scale (all the dimensions and the total score). There are no statistically significant differences between the mean scores of the males and the females on the optimism scale. There are no statistically significant differences between the mean scores of the males and the females on all the dimensions and the total score of the psychological immunity scale except the fourth dimension (resilience and psychological rigidity) and the eighth dimension (adaption and psychological resilience). There are statistically significant differences in favor of the females. There are no statistically significant differences between the mean scores of literary and scientific disciplines in the first dimension (self-image), the third dimension (looking into the future) and the total score on the optimism scale. There are statistically significant differences on the second dimension (looking at events and others) in favor of the scientific disciplines. There are no statistically significant differences between the mean scores of the literary and scientific disciplines in all the dimensions and the total score of the psychological immunity except the third dimension (self-control) in favor of the scientific disciplines. The results also indicated that we can predict the total score of the psychological immunity through the dimensions scores of the optimism scale among the university students. The thesis recommends the necessity of increasing optimism among university students as it's a positive factor that contributes to achieving a better level of mental health. It also suggests preparing a program to enhance and activate the psychological immunity among university students.