Secondary, non-inflammatory osteoarthritis (OA) is a common disorder in dogs. Its silent onset prevents early diagnosis and delays treatment. Synovial fluid biomarkers can detect OA at an early stage, before the presence of radiographic signs. In addition, these local biomarkers can aid prognosis of the disease, monitor the response to treatment and can be used to assess the degree of OA. Currently three groups of canine synovial fluid biomarkers have been the focus of research: proinflammatory mediators, enzymes and their inhibitors, and extracellular cartilage degeneration products. These have been investigated in the elbow, hip and stifle joints of both normal dogs and dogs with naturally occurring and experimentally induced OA. None of these biomarkers are currently used in practice for the detection of canine OA at an early stage. A positive relationship between canine synovial fluid biomarkers and OA has been demonstrated, yet no molecular diagnostic test has been developed so far.