BACKGROUND: In this study, we aimed to compare the efficacy of corticosteroid trigger point injection (TPI) versus extracorporeal shock wave therapy (ESWT) on inferior trigger points in the quadratus lumborum (QL) muscle. METHODS: In this single-blind randomized clinical trial, 54 low back pain patients with myofascial trigger points on QL muscle were investigated. Participants were randomly allocated into two groups with A and B pockets. Patients in group A underwent radial ESWT and received 5 treatment sessions (1 per week) and actually were not followed-up. However, patients in group B received corticosteroid TPI and received one session of corticosteroid treatment and followed-up for 4 weeks after injection. Oswestry Disability Index (ODI), visual analogue scale (VAS), pain pressure threshold (PPT) and short form (36) health survey (SF-36) were measured in both groups before, two weeks after and four weeks after intervention. RESULTS: The between group comparison indicated that corticosteroid TPI leaded to significant higher improvements of ODI (P-value< 0.01), VAS (P value< 0.001), and PPT (P-value = 0.001) scores compared to the ESWT group at two-week follow-up time-point. ESWT group recorded significant higher improvement of ODI (P-value< 0.01) and SF-36 (P-value< 0.001) compared to the corticosteroid TPI at 4th week post treatment evaluation. At four-week follow-up time-point, the patients in the ESWT group were 1.46 times more likely to achieve 30% reduction in VAS, 2.67 times more likely to achieve 30% reduction in ODI, and 2.30 times more likely to achieve 20% improvement in SF-36 compared to the participants in corticosteroid TPI group. These results refer to large effect size for all study outcomes in ESWT group (d = 4.72, d = 1.58, d = 5.48, and d = 7.47 for ODI, PPT, SF-36, and VAS, respectively). CONCLUSION: Corticosteroid TPI was more effective compared to ESWT in short-term controlling of pain and disability caused by myofascial pain syndrome of QL muscle. However, after 4 weeks treatment, ESWT further improved the quality of life and disability and was related with more probability of achievement the minimal clinically important difference concerning pain, disability and quality of life and large effect size for all study outcomes in treated patients compared to corticosteroid TPI. TRIAL REGISTRATION: www.irct.ir , IRCT20100827004641N14 , retrospectively registered 2019-01-19.