Objective:To investigate the expression and significance of β-catenin in different times of synovial tissue of osteoarthritis SD rat models. Methods: Ninty SD rats were divided into experimental and control groups randomly. The anterior cruciate ligament(ACL) was cut off to establish a experimental model,the treatment of control group was similar to the experimental group,transction ACL. Rats were sacrificed at 4,8 and 12 weeks after surgery,the synovial tissue wore obtain,and the expression of protein and gene of β-catenin was measured by immunohistochemistry (IHC) and semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR)in different times of experimental groups and control groups. Results: Results from IHC showed that β-catenin was expressed in all experimental rats,and the expressions of β-catenin 4/8/12 weeks were different (all P < 0.05). The expressions of β-catenin in 4 and 8 weeks were not different in control groups,and the expression of β-catenin was positive in part of the control group in 12 weeks. Semi-quantitative RT-PCR showed that the expression of β-catenin in the experimental group was higher than that of the control group,and the expression increased with the extension of time in the experimental group,and the expression of β-catenin of control groups were different 4/8/12 weeks among (P < 0.05). Conclusion:β-catenin was expressed in the synovial tissue of OA at a high level. And its level was increased with the extension of time,which indicates that. β-catenin plays a critical role in the pathogenesis and progression of osteoarthritis.