[Purpose] The aim of study was to compare different durations of ultrasound in patients with knee osteoarthritis. [Subjects and Methods] One hundred patients diagnosed with bilateral knee osteoarthritis (OA) were enrolled in this study. Patients were divided into two groups. The first group (G1) received 4 minutes of ultrasound. The second group (G2) received the exact same treatment, but the duration of ultrasound was longer at 8 minutes. Patients in both groups underwent a total of 10 ultrasound over 2 weeks. Following treatment, all patients provided self-evaluations of pain via the Visual Analog Scale (VAS), overall physical function with WOMAC, disability via the Lequesne index (Leq), and depressive symptoms with the Beck Depression Index (BDI). [Results] There were no significant differences in VAS, WOMAC Leq, and BDI values between groups 1 and 2. After treatment, VAS, WOMAC, Leq, and BDI values improved for both treatment groups. However, following treatment, G2 had significantly greater values for WOMAC functional and total scores than G1. No statistically significant differences were observed for VAS scores while inactive, WOMAC pain and stiffness scores, and BDI values after treatment between both groups. VAS pain scores while active and Leq index values were significantly lower in G1 than G2. [Conclusion] Patients in both groups demonstrated improved functionality, pain and psychological status following a consistent, 2-week regimen of 4-minute or 8-minute treatments with ultrasound. Yet, patients that experienced longer treatment durations of 8 minutes demonstrated better outcomes in pain and the ability to carry out activities of daily living.