INTRODUCTION: Acute low back pain is one of the most common health problems especially in industrialized countries where 75 per cent of the population develop it at least once during their life. This study examined the efficacy of thermotherapy and cryotherapy, alongside a routine pharmacologic treatment, on pain relief in patients with acute low back pain referring an orthopedic clinic in Shahrekord, Iran. MATERIALS AND METHODS: This clinical trial study was conducted on 87 patients randomly assigned to three (thermotherapy and cryotherapy as intervention, and naproxen as control) groups of 29 each. The first (thermotherapy) group underwent treatment with hot water bag and naproxen, the second (cryotherapy) group was treated with ice and naproxen, and the naproxen group was only treated with naproxen, all for one week. All patients were examined on 0, 3(rd), 8(th), and 15(th) day after the first visit and the data gathered by McGill Pain Questionnaire. The data were analyzed by SPSS software using paired t-test, ANOVA, and chi-square. RESULTS: In this study, mean age of the patients was 34.48 (20-50) years and 51.72 per cent were female. Thermotherapy patients reported significantly less pain compared to cryotherapy and control (p≤0.05). In thermotherapy and cryotherapy groups, mean pain in the first visit was 12.70±3.7 and 12.06±2.6, and on the 15(th) day after intervention 0.75±0.37 and 2.20±2.12, respectively. CONCLUSION: The results indicated that the application of thermo-therapy and cryotherapy accompanied with a pharmacologic treatment could relieve pain in the patients with acute low back pain.