Collagen supplements have gained significant market popularity, with numerous products claiming to improve knee osteoarthritis symptoms. Previous clinical studies have primarily evaluated individual collagen formulations, with most being industry-sponsored, which raises potential bias concerns. This study aimed to evaluate the efficacy of combined undenatured type II collagen (UC-II) and hydrolysed collagen supplementation in patients with knee osteoarthritis. In this randomised, double-blind, placebo-controlled trial, 68 patients with knee osteoarthritis were divided into two groups: one receiving collagen supplements (tablets containing hydrolysed collagen and UC-II) and the other receiving a placebo. Clinical outcomes, including pain intensity (Verbal Numerical Rating Scale), functional outcomes (Knee Injury and Osteoarthritis Outcome Score [KOOS]), rescue medication consumption, and patient satisfaction, were assessed at baseline, 2, 6, and 12 weeks. Baseline demographic characteristics were comparable between the collagen and placebo groups. Both groups showed significant improvements in pain intensity (p < 0.001) and KOOS scores over time. However, no significant differences were observed between the groups in terms of pain intensity, functional outcomes, rescue medication consumption, or patient satisfaction (p > 0.05). No adverse effects were reported in either group. Combined UC-II and hydrolysed collagen supplementation over 12 weeks did not demonstrate superior efficacy compared with that of the placebo in managing knee osteoarthritis symptoms. Further research is required to explore the potential long-term benefits of combined collagen supplementation.Clinical Trial Registration: ClinicalTrials.gov (NCT06229951): registered on January 16, 2024.