Background. Surgical treatment and conservative treatment is the options to improve pain, function, and range of motion following rotator cuff tear. In this study, we aimed to compare the effects of physiotherapy and corticosteroid injections on the function, pain, and range of motion in patients with full-thickness rotator cuff tearing separately and simultaneously. Methods. A total of 96 patients were randomly assigned to the study and divided into 3 groups of 32 patients. DASH questionnaire and VAS criterion were completed by all three groups, and the range of motions of all groups was measured by a goniometer. Then, the first group underwent 12 sessions of physiotherapy twice a week for 6 weeks; the second group received 80 mg of methylprednisolone and 1 ml of lidocaine 2% in two stages, 21 days apart; and the third group received 80 mg of methylprednisolone and 1 ml of lidocaine 2%, and after 2 days, 6 sessions of physiotherapy twice a week for 3 weeks were prescribed. In the end, the questionnaire was filled out by the patient, and the range of emotions was assessed with a goniometer. Results. More than 80% of patients in each group were female. There was no significant difference between the gender and age distribution of the groups. The mean age in physiotherapy, steroid, and physiotherapy + steroid groups was 51.78 ± 7.37, 52.37 ± 6.61, and 50.87 ± 5.65, respectively. The combination of physiotherapy + steroid intervention was more effective in reducing VAS and DASH scores than physiotherapy or steroid injection alone. Goniometric findings showed that treatments that included the steroid injection approach (steroid injection and steroid + physiotherapy) had a more dramatic effect on improving the patients’ range of motion than physiotherapy alone. Conclusions. Among the conservative approaches of treating full-thickness rotator cuff tear, a combination of steroid injection and physiotherapy is more effective significantly in comparison with either treatment alone. This trial is registered with IRCT20200102045987N1.