Chronic liver injury, independent of the cause, is generally associated with the accumulation of matrix proteins, a process referred to as fibrosis. Over the last decade liver fibrosis is no longer viewed as either passive or permanent but as a dynamic process and potential therapies continue to be identified. Hepatic stellate cells (HSCs) play a critical role in the fibrogenesis of liver, so they are the target cells of antifibrotic therapy. Activated HSCs but not quiescent HSCs express cyclooxygenase-2 (COX-2). Peroxisome proliferator activated receptor gamma (PPAR gamma) has been shown to be expressed in quiescent HSCs in the normal liver and decreased PPARγ expression has been associated with activation of HSC. The present study was designed to investigate the possible prophylactic and therapeutic effects of a selective COX-2 inhibitor (celecoxib) and a synthetic PPAR gamma ligand (pioglitazone) on liver fibrosis induced by thioacetamide (TAA) in rats.