The canine Rheumatoid Arthritis (RA) is an uncommon disturbance, which results in erosive polyarthritis and progressive articulation destruction. Small breeds and miniatures spanning from nine months to 13 year-olds are the most affected. The etiology is unknown, but there is a belief that it is related to immune reaction against endogenous antigens forming articular immunocomplexes. Claudication, member diversion and soft tissue tumefaction around articulations leading to crepitation, laxity, dislocation and articular deformities affecting mostly carpus, tarsus and phalanges are the forms of manifestation. Additional exams are osteoarticular radiographies, arthrocentesis and serology. Hemogram and synovial culture present no alterations. At biopsy increased synovial thickness, hyperplasia and synovitis proliferation can be observed. Previous treatment slows down the progression of the disease and is based on immunosuppressive drugs and chondroprotective. The prognosis is not good. This work has the objective of reporting a clinical case of RA, elucidating the importance of the diagnosis. An eight year-old male canine mongrel, was attended at the Veterinary Hospital at the University Center of Vila Velha, presenting as main complaint, reported by a colleague, neurological alteration showing locomotor and stand by difficulty for five months. Physical exams showed brachycephalic syndrome in addition to musculoskeletal processes, plantigrade walk, sensibility and crepitation at palpation of all members and distal articulations. The radiographies of humerus-radio-ulnar, carpus and interphalangeus articulations were compatible with erosive polyarthritis evidenced by loss of bone density, areas of osteolysis, deformity of articular spaces, bone and articular irregularities. Xanthochromic synovial fluid, odorless and turbid, with mononuclear cells, composed by high activity phagocytes, rare osteoclast and amorphous phagocytic material, was observed at arthrocentesis, suggesting chronic degenerative articular disease. The animal had already been treated with Meloxicam® and at the moment is being treated with Chondrotin®, Meticorten® and physiotherapy. Two months after the beginning the treatment, the animal has had an improvement on the ambulation and a relief of the pain, having continued with clinical and physiotherapeutic monitoring. The prognosis is unfavorable, but in this case it was observed that despite its chronicity, the correct treatment along with physiotherapy reduced the pain and the progression of the disease to the others members, improving the patient's quality of life. Therefore the importance of a judicious physical exam along with information from differential diagnosis and additional exams should be highlighted for a definitive diagnosis, since an early diagnostic can reduce the progression and improve canine quality of life.