Background: Myofascial release (MFR) technique is frequently used in musculoskeletal problems. There are many studies of the MFR technique on the diaphragm or iliopsoas muscle. However, no studies in the literature performed both diaphragmatic and iliopsoas MFR techniques in patients with chronic low back pain. Objective: To investigate the effects of diaphragmatic and iliopsoas MFR techniques on pain, lumbar spine range of motion (ROM), chest wall mobility, and flexibility in patients with chronic low back pain. Design: Randomized controlled clinical study. Participants: Forty-two participants with chronic low back pain, aged between 20 and 50 years. Intervention: The sample was randomly allocated into one of two groups; the myofascial group (n = 21) and control group (n = 21) received the MFR technique or the placebo MFR technique as a complementary therapy to traditional physiotherapy treatment. Outcome measures: Primary outcomes were pain, chest wall mobility, lumbar spine range of motion (ROM), and flexibility. Secondary outcomes were depression, kinesiophobia, and functional disability. Results: The MFR techniques significantly reduced the pain, with a between-group difference of -2.05 (95% CI, -2.93 to -1.15) for rest, -2.62 (95% CI, -3.34 to -1.89) for trunk flexion, and -2.00 (95% CI, -2.84 to -1.16) for trunk extension in favor of the EG. MFR techniques significantly increased the lumbar spine ROM after interventions, with a between-group difference of 16.67° (95% CI, 8.87 to 24.47) for flexion, 7.63° (95% CI, 5.44 to 9.80) for extension and, 9.53° (95% CI, 6.57 to 12.48) for right lateral flexion. There was also a significant difference between the groups in flexibility in favor of the MG of 1.95 cm (95% CI, 1.41 to 2.49) for MST, -13.52 cm (95% CI, -20.18 to -6.86) for trunk flexion and, -4.37 cm (-6.50 to -2.28) for right lateral flexion The MFR techniques also significantly increased the chest wall mobility after interventions, with a between-group difference of 2.52 cm (95% CI, 1.82 to 3.23) for the xiphoid region and 3.48 cm (95% CI, 2.60 to 4.36) for the subcostal region. Conclusion: Diaphragmatic and iliopsoas MFR techniques may be effective in pain, lumbar spine ROM, flexibility, and chest wall mobility in patients with chronic low back pain.