Collagen is an extracellular matrix protein present in the skin, tendon, cartilage and bone. Collagen peptides (CP) are produced by the hydrolysis of gelatin (heat-denatured collagen) by proteases and are utilized as a component of nutraceuticals. The current study investigated the effect of CP on the articular cartilage of OA by evaluating the serum levels of biomarkers (CTX–II for type II collagen degradation and CPII for type II collagen synthesis), histopathological changes (Mankin score, based on the toluidine blue staining of proteoglycans), and immunohistochemical staining of matrix metalloproteinase (MMP)-13 and type II collagen, using a rat experimental osteoarthritis (OA) model. Anterior cruciate ligament transection (ACLT) was performed on the right knee joint to surgically induce OA. Animals were divided into four groups: Control group (Control), sham-operated group (Sham), ACLT group without collagen peptide (ACLT group) and ACLT group with oral administration of CP (CP group). ACLT induced histological damages and significantly increased the Mankin score (P<0.05). However, CP administration markedly suppressed the Mankin score, although this difference was not significant. In addition, serum CTX-II levels were significantly decreased in CP group compared with those in the ACLT group (P<0.05). By contrast, serum CPII levels did not differ significantly among the four groups. Moreover, immunohistochemical staining of type II collagen and MMP-13 (an important type II collagen-degrading enzyme) indicated that the amount of type II collagen increased, whereas the number of MMP-13 positive chondrocytes decreased in the CP group compared with ACLT group. These observations suggest that CP has the potential to exert chondroprotective action on OA by inhibiting MMP-13 expression and type II collagen degeneration.