Aseptic arthritis of the knee joint was induced in 12 healthy donkeys, weighing 60 to 85kg by intra- articular injection of 0.3ml of turpentine oil. The animals were randomly divided into 2 groups A and B of 6 animals each. Group A served as a control whereas in Group B anti-arthritic drug, diclofenac sodium (Diclocare 5%) was administered intramuscularly at the dose rate of 2.5mg/kg body weight daily for 5-6 days starting one day after the induction of arthritis. In group B, the joint circumference became normal on 6th day after induction of arthritis while in group A (control), the joint circumference took 16 to 20 days to become normal. According to this trial, diclofenac sodium provided an early return to normal stance and weight bearing in treated group B, taking longer time in control group A. No significant change in blood Haemoglobin, Total erythrocyte count, Total leukocyte count, Erythrocyte sedimentation rate and Packed cell volume was observed in control and treated animals. It is concluded that diclofenac sodium is an effective treatment for arthritis in donkeys.