Background: Low Intensity Pulsed Ultrasound (LIPUS) is beneficial in accelerating fracture recovery, enhancing their capacity to execute tasks of daily life and, as a result, their autonomy. Methods: Thirty-four (29 males and 5 females) pre-diagnosed patients referred by an orthopaedic surgeon exhibiting symptomatic low back pain for at least four months were recruited and randomly divided into LIPUS group and Routine Physical Therapy (RPT) group. The lottery method was used to randomly assign patients into two groups. Numeric Pain Rating Scale (NPRS) was utilized for the measurement of pain and Oswestry Disability Index (ODI) for functional disability. Patients were assessed at baseline, at the end of 12th and 20 th week. Interventions were applied by the physical therapist having more than eight years of clinical experience for 10 weeks on alternate days. Results: LIPUS group reported greater reduction in pain with mean change of 3.18 points (95% CI: 2.2, 4.2; p < 0.001) at 12 th week, 6.18 points (95% CI: 5.5, 6.8; p < 0.001) at 20th week follow-up and functional disability with mean change of 28.24 points (95% CI: 23.7, 36 32.8; p < 0.001) at 12th week and 39.47 points (95% CI: 31.8, 47.1; p < 0.001) at 20th week follow-up compared with the RPT group.Conclusion: Low-intensity pulsed ultrasound has significantly reduced pain and functional disability in patients with early-stage lumbar spondylolysis and could be preferred as a safe non-invasive treatment method for early bone healing. Trial registration: WHO-Iranian registry of clinical trials (IRCT20200206046396N1, Dated: 02/05/2020).