Knee osteoarthritis (OA) is the most prevalent degenerative musculoskeletal disorder, which is particularly common in older population. While conventional treatments have limited effectiveness, the development of more effective therapeutic strategies is necessary to address this primary source of pain and disability. Umbilical cord mesenchymal stromal cells (UC-MSCs) offer a promising therapeutic approach for treating knee OA.This randomized, prospective, double-blind and controlled pilot study was carried out to evaluate and compare the safety and therapeutic efficacy of a single intra-articular injection of a standardized product CellistemTMOA (5 × 106 ± 5 × 105 UC-MSCs), vs. triamcinolone (a synthetic corticosteroid) (10 mg/mL) in thirty patients with symptomatic knee OA (Kellgren-Lawrence grade II or III).The outcomes included changes in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores based on a Likert scale, numerical rating score (NRS) for pain, Magnetic Resonance Imaging (MRI), and quality of life (SF-36 questionnaire), from baseline and throughout 12-months of follow-up.Patients treated with CellistemTMOA showed significant improvement in WOMAC score (including the three subscale scores (pain, stiffness and function), NRS in pain, and SF-36 profile from baseline to 12 months (p < 0.05) compared to the triamcinolone group, and no severe adverse events were reported.There were no significant differences in MRI WORMS scores between the two groups. However, patients who received the cellular treatment experienced a significant improvement in their SF-36 profile (p < 0.05).This pilot study revealed that a single dose of CellistemTMOA is safe and superior to the active comparator in knee OA at 1-year of follow-up, making it a compelling therapeutic alternative to treat symptomatic OA patients.