Objectives: This study aimed to investigate the effects of different carrier frequencies of interferential current (IFC) treatment on a Visual Analog Scale (VAS) for pain, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), 10-m walk test, and the amount of paracetamol taken. Patients and methods: The double-blind, randomized controlled study included 61 patients (16 males, 45 females; mean age: 63.7±9.8 years; range, 50 to 80 years) with knee osteoarthritis who were randomized to three treatment groups: 2,000 Hz, 4,000 Hz, and 8,000 Hz. The study was conducted between February 2019 and October 2019. Subjects received IFC treatment for 20 min five times per week for three weeks. All subjects were prescribed a home exercise program. Patients were evaluated at baseline and at three and seven weeks. The primary outcome was VAS to assess knee pain. Results: Treatment with IFC yielded significant results in VAS pain, WOMAC pain, and WOMAC function parameters in all three groups, but no significant difference was shown among the three groups. The WOMAC stiffness parameter was found to benefit from the treatment only in the first group, while the 10-m walk test improved for the first and third groups. The number of paracetamol tablets taken differed significantly neither in nor among the treatment groups. Conclusion: Previous trials have found a significant reduction in knee pain levels and an increase in function with IFC treatment, although there is no consensus on which carrier frequencies and duration to choose for IFC treatment. In this study, we detected significant benefits for all the different carrier frequency groups but were not able to show any to be superior to the others.