Introduction: The treatment process of hospitalized patients with obsessive-compulsive disorder is less studied. However, because of the complex nature of the disease, these patients require a comprehensive nursing care plan. Since nursing process based on Roy's adaptation model is widely used to solve problems caused by chronic diseases, this study aimed to implement this model in a patient with obsessive-compulsive disorder. Methods: This study was a case study performed on a patient with obsessive-compulsive disorder admitted in the psychiatric ward of Farshchian (Sina) Hospital in Hamadan, Iran, in 2019. Data were collected using observation, interview, and patient documentation, and they were analyzed in four dimensions based on the stages of the nursing process in Roy's adaptation model. Results: Based on data from the assessment stage, manifestations of chronic maladaptive behaviors in the patient included unwanted, intrusive, repetitive thoughts and fears as the focual stimuli, family history of obsessivecompulsive disorder, parental divorce and weakness in coping mechanisms as the contexcual stimulus, beliefs of the patient's father, and psychiatric hospitalization as residual stimuli. Six types of maladaptive behaviors in four modes including inappropriate nutrition (physiological mode), reduced self-care, non-adherence to treatment, need to perform obsessive rituals, avoiding social interactions (self-concept mode), and father dependency (role function mode and interdependence mode) were identified. Conclusions: Implementing a nursing process based on Roy's adaptation model by deeply identifying maladaptive behaviors and then, promoting the use of regulate and cognitive coping mechanisms can help correct or modify maladaptive behaviors of patients with obsessive-compulsive disorder. However, achieving desirable outcomes after discharge requires long-term follow-up and support by psychiatric nurses.