Knee joint pain is a common cause of disability, with risk factors including aging, obesity, and occupational joint loading. Because long-term use of conventional analgesics can lead to adverse effects, low-risk nutraceutical options are of growing interest. Undenatured type II collagen (UC-II) has shown symptomatic benefit in randomized trials, while glucosamine and curcumin have demonstrated pain-reducing, synovial-supporting, and anti-inflammatory effects in systematic reviews. In this study, we evaluated the efficacy of a UC-II+glucosamine+curcumin combination for reducing knee joint pain and improving function. A two-arm, parallel-group, randomized, double-blind, clinical trial enrolled 32 adults with knee pain who received either a placebo or the test product for 12 weeks (two capsules daily). The capsules of the placebo group contained UC-II only, whereas those of the test group contained UC-II, glucosamine, and curcumin. Assessments at weeks 0, 6, and 12 included a visual analog scale (VAS), timed up-and-go (TUG), active/positive range of motion (AROM/PROM), and the Western Ontario and McMaster Universities Arthritis Index (WOMAC). Both groups showed improvements in knee pain. In the test group, the TUG time significantly decreased and knee ROM increased by week 6. Supplementation with the UC-II+glucosamine+curcumin combination was associated with observable pain reduction and functional improvement of the knee joint.