Introduction: Multiple sclerosis (MS) is a common non-communicable disease that paralyzes the immune system. Obsessive-compulsive disorder leads to rumination and repetitive actions that increase anxiety, worries and stress in people with this disease. The aim of this study was to identify the lived experiences of MS patients with obsessive-compulsive disorder. Methods: The present study was conducted with a descriptive phenomenology method. The participants of the study were patients with multiple sclerosis who referred to Noor Laboratory in Tehran in 2020. According to the end of the study, the data collection method was performed by semi-structured interview. The sampling method was purposeful. The sampling was theoretically saturated by interviewing 15 participants. Data were analyzed using Colaizzichr('39')s seven-step Method. Results: Data analysis indicated that the three main themes were: "Childhood and family member’s experiences underlying obsessive-compulsive disorder", "Disturbing thoughts and emotions about the disease and it’s treatment" and " experience uncertain future ". Conclusion: The findings showed that patients with multiple sclerosis experience various stresses, mental conflicts and obsessive-compulsive disorder. Identifying the behaviors and thoughts of OCD in these patients helps the process of evaluation, diagnosis and psychological treatment and interventions of obsessive-compulsive disorder and ultimately, helps them to improve their mental health and quality of life.