Objective: The aim of this study was to evaluate the effects of low level laser therapy (LLLT) on the degenerative process in the articular cartilage after an anterior cruciate ligament transection (ACLT) model in rats. Methods: Eighty male rats (Wistar) were divided into four groups: 1.) intact control group (CG), 2.) injured control group (ICG), 3.) injured laser-treated group at 10 J/cm 2 (L10) and 4.) injured laser-treated group at 50 J/cm 2 (L50). Animals were divided into 2 subgroups, with different periods of sacrifice (5 and 8 weeks post-surgery). The ACLT was used to induce osteoarthritis (OA) in the knees of the rats. LLLT started 2 weeks after the surgery and it was performed for 15 and 30 sessions, respectively using a 685-nm laser, at 10 and 50 J/cm 2 . Qualitative and semi-quantitative histologic, morphometric and immunohistochemistry analyses were performed. Results: Initial signs of tissue degradation could be observed 5 weeks post-ACLT, evidenced by the decrease of proteoglycan concentration and increase in cartilage thickness of the ICG. After 8 weeks post-surgery, analysis showed a progression of the degenerative processes in the ICG revealed by the increased cellularity and higher TNF-α, IL1-β and MMP-13 immunoexpression. LLLT was able to modulate some of the aspects relating to the degradative process, such as biomodulation of the number of chondrocyte proliferation, prevention of proteoglycan loss, and decrease of MMP-13 immunoexpression. Conclusion: This study showed that the 685-nm laser irradiation, especially at 10 J/cm 2 , prevented features related to the articular degenerative process in the knees of rats.