Background and aim: Osteoarthritis (OA) is a common disease with unknown causes which is related to the age and is more common in middle and older age. The aim of this study was to evaluate the effect of bone marrow derived mesenchymal stem cells (BM-MSCs) and secreta in healing of induced OA in guinea pig. Methods: BM-MSCs were extracted from guinea pig bone and cultured. OA was induced by cutting the anterior cruciate ligament in 15 guinea pigs. Then, 106 BM-MSCs at 3rd passage were administered to 5 animals, secreta was injected to 5 other and 5 were kept as the control group as untreated. After three months, the healing processes were evaluated by testing of histopathology and radiological parameters. Results: The radiological assessment showed a significant reduction of OA in stem cells and secreta groups in comparison to the control group (P<0.05). Also, OA histological feature in stem cells and secreta groups was better than control group. However, the matrix distribution of articular cartilage and collagen types 1 and 2 in secreta group were significantly better than other groups (P<0.05). Conclusion: Our results showed that the use of BM-MSCs and their secreta in treatment of OA was associated with reduction of radiological and histological index of OA.