Problem statement: There are indications that the intake of gelatin hydrolysate has a beneficial impact on the clinical signs of osteoarthritis in dogs. Data from a controlled trial were required to substantiate these indications. Approach: A double-blind, placebo-controlled trial with privately owned dogs was carried out to assess the efficacy of a preparation of gelatin hydrolysate in the treatment of osteoarthritis. With the use of a questionnaire, the clinical signs were evaluated by the owners. For a period of 8 weeks, the test dogs daily received 10 g of gelatin hydrolysate; as a placebo, soya protein isolate was used. The supplements were mixed with the diet; all dogs were fed on the same dry food. There were 15 dogs per treatment group. Results: The administration of gelatin hydrolysate significantly improved activity (vitality) and significantly reduced stiffness and lameness. Conclusion: Gelatin hydrolysate is commonly used as a component of human foods and is generally considered as safe. It is suggested that a dose of about 2.5% in a dry food would be beneficial for dogs with osteoarthritis.