Objective: There are some electrotherapy studies regarding transcutaneous electrical nerve stimulation (TENS) and interferential current therapy (IFT), but none have examined their synergistic effects. This investigation was performed to assess the effectiveness of TENS/IFT in relieving chronic low back pain (LBP). Material and Methods: In this double-blind, placebo-controlled study, a total of 123 patients were divided into four groups using a computer method. Group 1 received TENS, Group 2 IFT, Group 3 combined TENS/IFT, and Group 4 sham TENS/IFT five times a week for 3 weeks. All participants also received hotpack therapy. Lumbar range of motion (ROM) was assessed via an inclinometer and the modified Schober test, and pain during activity was evaluated using a Visual Analog Scale (VAS) along with patient and physician global assessments. The Rolland-Morris Disability Questionnaire (RMDQ) was administered to determine functional capacity. Results: Groups 1, 2, and 3 showed significant improvement, but Group 4 showed none (p˂0.001). Group 3 was superior to Group 2 with regard to the RMDQ, VAS, and global assessments (p˂0.001). Conclusion: Combined TENS/IFT was more effective than IFT in improving functional level and decreasing pain during activity in patients with chronic LBP, however it was not superior to TENS therapy alone. The findings of this study offer insight that can be applied to future investigations concerning combined TENS/IFT therapy with different application frequencie and modes or other combined therapies. We observed marked improvement in function and pain during activity with the combination of both therapies; however, improvement was not significantly greater to that achieved with TENS therapy alone. Combined therapy was also superior to the other treatments with respect to doctor and patient global assessments, but this was not significantly different compared with that in the TENS and IFT alone groups. No improvements were found in the control (sham) group.