Background: Multiple sclerosis (MS) is the most common disabling disease of the central nervous system. In these patients, fatigue is the most common symptom that causes disorder in the work, social activities and daily functions of the patients. Given the assumption that MS reduces the patients′ psychological well-being, this study aimed at assessing the psychological well-being of both the patients and their primary caregivers. Materials and Methods: Current research as a descriptive study was conducted on 200 MS patients and 200 primary caregivers. For data collection, the Reef questionnaire was used to determine psychological well-being of these individuals. Data were analyzed using SPSS software. Results: According to the obtained results, the mean duration of MS was estimated 6.37 years. The psychological well-being score of the people with MS and their primary caregivers was slightly higher than average. The total score of psychological well-being in primary caregivers was higher than the patients. Conclusion: The mean score of psychological well-being subscales was significantly different in patients and their caregivers. Regarding the autonomy subscale, there was a significant different in patients with MS, that is, it was lower than average. In terms of two subscales of "positive relationship with others" and "personal growth," there was no difference between people with MS and the primary caregivers, and for other subscales, the mean score of caregivers was higher than the patients.