ABSTRACT Introduction & Background: Spiritual intelligence has a major role in provision and promotion of mental health. The importance of happiness in social participation, physical and mental health cannot be ignored, and it is one of the most important priorities of psychology. The purpose of the study is to examine the relationship between happiness and spiritual intelligence in the nursing students of Shiraz and Tehran University of Medical Sciences. Methods: This is a descriptive crosssectional study and the population consisted of nursing students of Shiraz and Tehran University of Medical Sciences. Oxford happiness and spiritual intelligence questionnaires were used in this study and data analysis was conducted using SPSS 22 software. The study population comprised 541 nurses from nursing students of Shiraz and Tehran University of Medical Sciences. Of these, 394 students from Shiraz and 147 from Tehran were selected. Results: The mean score of active wellbeing for 5 happiness components of the two cities was statistically significant (P<0.001). The ratio of problem coping between 4 components of spiritual intelligence was significantly different (P<0.001). Also, there was a significant difference between the scores of spiritual intelligences in the employed and non- employed students (p<0.013). Conclusion: According to the results, students with higher levels of spiritual intelligence were happier because these components are linked to mental health. The results of this study can help improve the mental health performance for students in hospitals. It can also consider solutions for improving spiritual intelligence and personal life of university students.