The study was designed to identify the relationship between existential vacuum and psychological hardiness in a sample of Nizwa University students in the Sultanate of Oman. The study sample consisted of (498) male and female students. The researcher followed the correlative descriptive method. The researcher used to measure the existential vacuum variable Mustafa scale (2013), and the scale of Makhaimer (2015) in measuring the variable mental hardiness. The study concluded that the level of Existential Vacuum in the sample of the study was low, while the level of psychological hardiness in the sample of the study was high. The study also showed a statistically significant and negative correlative relation between the level of the existential vacuum and the level of psychological hardiness. As for the cumulative average variable, the study showed that there were statistically significant differences in the existential vacuum and it was in favor of students of excellence with honors. However, as for the variable of psychological hardiness, the results revealed that there were no statistically significant differences in the psychological hardiness due to the variables of sex and specialization. The study concluded that the existential vacuum attributes with a rate of (37.5%) in the interpretation of variation in mental hardiness.