OBJECTIVE: To compare the efficacy of interferential current (IFC) therapy combined with quadriceps strengthening exercise versus sham IFC plus exercise for pain relief and functional improvement in patients with knee osteoarthritis. STUDY DESIGN: Double-blind randomised controlled trial. SETTING: Outpatient rehabilitation clinic. SUBJECTS: Knee osteoarthritis patients aged 50-85 years with a pain score ≥4/10. METHODS: One hundred forty-four participants were randomly allocated into the study and control groups. The study group received 20 min of IFC therapy (carrier frequency: 4000 Hz, beat frequency: 100 Hz) five times per week for three weeks, while the control group received sham IFC following the same protocol, followed by 10 min of exercise in both groups. Outcome measures included Numeric Rating Scale for Pain, Western Ontario and McMaster Universities Index (WOMAC) score, gait speed, and EuroQol-Five Dimensions-Five Levels questionnaire assessed at baseline, Week 3, and Week 6. Adverse events and patient satisfaction were evaluated at Week 3. RESULTS: At Week 3, the study group demonstrated statistical improvement compared to the control group for Numeric Rating Scale for Pain, WOMAC Total, WOMAC Pain, and WOMAC Stiffness. The mean difference (95% confidence interval) between groups was 0.76 (0.21-1.30), 0.49 (0.03-0.95), 0.63 (0.13-1.13), and 0.62 (0.04-1.20), respectively. However, the mean differences between groups were below the Minimally Clinically Important Difference values for each outcome. Additionally, there were no significant differences between groups at Week 6 for any outcome measure. CONCLUSION: IFC had no effect on pain reduction and functional improvement in patients with mild to moderate knee osteoarthritis.