To investigate plasma tumor necrosis factor-alpha (TNF-alpha) levels as an indicator to reflect the magnitude of the destructive inflammatory phase and articular cartilage damage after a knee trauma. Eighteen mature Wistar Albino male rats were divided into two groups equal in number. Nine animals underwent anterior cruciate ligament transection (ACLT) of the right knees, while nine animals had a sham procedure. All animals were killed at the end of 8 weeks; serum TNF-alpha levels were analyzed with enzyme linked-immunosorbent assay, and the osteoarthritic changes of articular cartilage were evaluated by a histopathological method using OARSI (Osteoarthritis Research Society International) osteoarthritis cartilage histopathology assessment system score. Serum TNF-alpha levels and OARSI scores showed significant difference between two groups. Despite 8 weeks after the initial trauma, ACLT group still demonstrated elevated levels of plasma TNF-alpha indicating the ongoing inflammatory phase. Serum TNF-alpha levels were also found to be correlated with the OARSI osteoarthritis cartilage histopathology assessment system scores. Post-traumatic local TNF-alpha overproduction as a proinflammatory cytokine is known to have a major role in cartilage matrix degradation. In this study, elevated plasma TNF-alpha levels were considered as the consequence of the early local inflammatory response to altered knee biomechanics. Degree of articular cartilage damage found to be consistent with plasma TNF-alpha levels suggest that monitoring plasma TNF-alpha levels may be a simple and reliable method to reflect the magnitude of destruction during the ongoing inflammatory phase of OA.