Introduction: Osteoarthritis (OA) of the knee causes disability due to pain and will affect the functional ability to walk. Low-Level Laser Therapy (LLLT) has been shown to reduce pain in knee OA, while High Intensity Laser Therapy (HILT) is able to reach deeper joint areas. Method: This study aimed to compare the effect differences between LLLT and HILT on pain and functional capacity in knee OA. Methods: This is a double-blind randomized controlled trial with 61 subjects randomized into LLLT (n=31) and HILT (n=30) groups. All the subjects were knee OA patient with Visual Analog Scale (VAS) ≥ 4. The laser therapy and exercise were given 3 times per week for 6 sessions. The pain scale evaluated using VAS and functional ability evaluated using 50-feet walk test. Result: After 6 sessions, both LLLT and HILT group showed reduced VAS score [∆VAS Score LLLT = 3 (2 – 4), HILT = 3 (2 – 5)] and increased walking speed (∆ walking speed for LLLT = 0.23 (0.02 – 1.24) m/s, HILT = 0.22 (0.08 – 0.7) m/s) which were statistically (p < 0.001) and clinically significant. HILT group had faster walking speed and greater VAS reduction compared to LLLT group (p < 0.001), but there was no significant difference in walking speed between two groups (p=0.655). Conclusion: HILT and LLLT combined with exercise were effective in reducing pain and increasing functional ability in knee OA after 6 sessions of intervention. Pain and functional ability improvement was faster and greater in HILT group than LLLT group.