The existing mechanisms of transcutaneous electrical nerve stimulation (TENS) focuses more on the effect of neural tissue. This study investigated the effect of TENS on the thickness of the erector spinae muscles and reducing pain. 56 individuals with low back pain participated in this single-blind, pre-posttest study. For two weeks, participants underwent ten sessions of TENS. The ultrasound evaluations examined the thickness of the erector spinae muscle, and the visual analog scale measured the severity of low back pain. There was a decrease in pain score and muscle thickness after the interventions (p ≤ 0.004). There was also a strong correlation between reducing pain and decreasing muscle thickness (R = 0.709; p = 0.000). Following TENS in the lumbar, in addition to reducing pain, the thickness of the erector spinae muscles also decreased. : IRCT20200423047173N1 (ClinicalTrials.gov).