The efficacy and tolerability of robenacoxib for the treatment of osteoarthritis in dogs were evaluated in a prospective, multicenter, randomized, noninferiority design clinical trial. A total of 32 dogs presenting with osteoarthritis were allocated randomly to receive, orally once daily for 28 days, either 1-2 mg/kg robenacoxib (n=21) or 3.5-5 mg/kg carprofen (n=11). Dogs were assessed by clinicians and owners using numerical rating scale scores at baseline and days 14 and 28. The primary efficacy endpoint was the global functional disability score, which was the sum of clinician scores for standing posture, lameness at walk, lameness at trot, willingness to raise the contralateral limb and pain at palpation. There was a good to excellent level of efficacy in both treatment groups. Differences between days 14 and 28 compared to day 0 were significant for all 11 clinician and owner scores for robenacoxib, and for 6 of 11 scores for carprofen. The efficacy of robenacoxib was numerically superior to carprofen for all 13 endpoints, but differences were not statistically significant. For the global functional disability score, the estimated efficacy of robenacoxib was 1.244 (95% confidence interval 0.555-2.493) relative to carprofen. The tolerability of both treatments was good as assessed from adverse events, clinical signs, and hematology and serum biochemistry variables. In conclusion, once daily administration of robenacoxib tablets had noninferior efficacy and tolerability compared to carprofen for the treatment of the clinical signs of osteoarthritis in dogs.