OBJECTIVE: Nonsurgical spinal decompression therapy (NSDT) is a conservative treatment for the lumbosacral herniated intervertebral disc (L-HIVD). This study aimed to evaluate the clinical effectiveness of the NSDT and change in disc volume through magnetic resonance imaging (MRI) in subacute L-HIVD. METHODS: Sixty patients with subacute L-HIVD were randomized into either the decompression group (group D, n = 30) or the nondecompression group (group N, n = 30). In group D, NSDT was performed ten times in eight weeks. In group N, pseudodecompression therapy (no force) was performed with the same protocol. Lower back and lower leg pain intensities and functional improvements were measured by the visual analog scale and the Korean Oswestry Disability Index (K-ODI). The change in the lumbosacral disc herniation index (HI) was evaluated through a follow-up MRI three months after the therapy. RESULTS: The lower leg pain intensity in group D was lower than that in group N at two months (p=0.028). Additionally, there were significantly lower K-ODI scores in group D at two and three months (p=0.023, 0.019) than in group N. The change in HI after the therapy was -27.6 +/- 27.5 (%) in group D and -7.1 +/- 24.9 (%) in group N, with a significant difference (p=0.017). Approximately 26.9% of patients in group D and no patients in group N showed over 50% reduction in HI (p=0.031). CONCLUSION: NSDT may be a suitable treatment option for conservative treatment of subacute L-HIVD.