Objectives: In this study, we aimed to evaluate the effectiveness of osteopathic visceral manipulation (OVM) combined with physical therapy in pain, depression, and functional impairment in patients with chronic mechanical low back pain (LBP). Patients and methods: A total of 118 patients with chronic mechanical LBP were assessed, and 86 who met the inclusion criteria were included in the randomized-controlled study between January 2021 and August 2022. The patients were randomized to either Group 1 (n=43), which underwent physical therapy (5 days/week, for a total of 15 sessions) combined with OVM (2 days/week with three-day intervals), or Group 2 (n=43), which underwent physical therapy (5 days/week, for a total of 15 sessions) combined with sham OVM (2 days/week with three-day intervals). Both groups were assessed before and after treatment and at the fourth week post-treatment. Results: Seven patients were lost to follow-up, and the study was completed with 79 patients (25 males, 54 females; mean age: 46.87±14.12 years; range, 19 to 75 years). Pain, depression, and functional impairment scores were all improved in both groups (p=0.001 for all). This improvement was sustained at week four after the end of treatment. However, improvement in the pain, depression, and functional impairment scores was significantly higher in Group 1 than in Group 2 (p=0.001 for all). Conclusion: The results suggest that OVM combined with physical therapy is useful to improve pain, depression, and functional impairment in patients with chronic mechanical low back pain. We believe that OVM techniques should be combined with other physical therapy modalities in this patient population.