Although normal synovial fluid has been well characterized in domestic animals such as dogs, cats, horses, and cows, the available information on larger rodents is scarce. Therefore, the aim of the present study was to analyze the physical, chemical and cytological characteristics of the synovial fluid in stifle joints of capybaras. Five free-ranging adult female capybaras (Hydrochoerus hydrochaeris), weighing from 37 to 56 kg, were used. Synovial fluid was obtained from aspiration of 10 stifle joints. Samples were analyzed for physical characteristics, chemical assays. Clotting was negative in nine samples. Most synovial fluid had pH 8, and values of protein were from 1.6 to 3.6 g/dL. The mucin clot test could be accomplished in six samples, all of which were classified as good. Nucleated cell numbers were from 140 to 508 cells/µL. Total differential cell count analysis demonstrated a predominance of mononuclear cells (97.6%), including 76.2% undifferentiated mononuclear cells, 18.1% macrophages, and 3.66% lymphocytes. Polymorphonuclear cells included 1.83% neutrophils and 0.2% eosinophils. In conclusion, the synovial stifle joint fluid of free-ranging capybaras is clear, colorless, viscous, and with chemical features and cytological findings that show some similarities with those seen in normal domestic animals.