This study evaluated the pharmacokinetic profile and therapeutic efficacy of piroxicam (PX), a long acting non-steroidal anti-inflammatory drug for the treatment of arthritis, following intra-articular (IA) injection in comparison to the pharmacokinetic profile and therapeutic efficacy of PX after intramuscular (IM) injection. In the pharmacokinetic study in rats, systemic exposure and pharmacokinetic parameters of PX after a single IA dose were compared with systemic exposure and pharmacokinetic parameters of PX after administration of the same dose IM (0.6 mg/kg). The anti-inflammatory and analgesic effects of IA PX were evaluated simultaneously in a monoiodoacetate-induced osteoarthritis rat model. The plasma PX concentration rapidly rose following IA injection, and it was comparable to the plasma PX concentration following IM injection, suggesting the rapid efflux of the drug molecule from the joint cavity. However, in the efficacy study, the IA PX administration significantly reduced the knee swelling by reducing the level of prostaglandin $E_2$ in the joint, compared to that following administration of IA vehicle and after administration of the IM PX dose. In addition, we found that the anti-inflammatory and anti-nociceptive efficacies of IA PX were synergistically increased upon co-treatment with hyaluronic acid (HA), a potent agent for the treatment of osteoarthritis, at the weight ratio of 1:1 or 1:2, and these effects were more pronounced than those following administration of HA or PX alone. In conclusion, this study demonstrated the efficacy of the IA use of PX alone and/or in combination with HA in osteoarthritis.