Background Most of the research on physical restraint is focused on determining patients’ experiences of restraint, the consequences of restraint, and healthcare professionals’ perceptions and attitudes. The aim of this study was to determine the opinions of the relatives of patients, who are a critical component of care, about physical restraint. The study used the mixed methods research approach, which combines quantitative and qualitative data collection methods. Method The study population consisted of 984 relatives of patients hospitalized in units where physical restraint was commonly applied between January 2018 and December 2018, and the sample consisted of 277 relatives of patients. The qualitative sample of the study consisted of 22 patient's relatives who were interviewed using the maximum diversity sampling method, a purposive sampling method. The quantitative data were analyzed using frequency, percentage, Chi Square (X2-Chi Square) test, and the qualitative data were analyzed using content analysis. Results The results showed that consent for physical restraint was generally obtained from spouses, physical restraint was applied to prevent self-harm, but relatives of the patients were insufficiently informed and worried about complications. It was also found that the most frequent reasons for physical restraint were self-harm and facilitation of treatment and care for the male patients and the feeling of helplessness for the female patients. Conclusion It was determined that the relatives of patients regarded physical restraint for treatment positively, but they were worried about complications, and they were mostly insufficiently informed before the intervention.