This study aims to investigate inflammatory changes and osteophyte formation in a rat osteoarthritis (OA) model longitudinally by using 7 T-magnetic resonance imaging (MRI) and micro-computed tomography (CT) . Method: This OA model is induced surgically by removing the medial collateral ligament and medial meniscus of the right knee joint. Using 7 T-MRI, we compared the relative signal value of the medial collateral site and the area (mm 2 ) of the upper end of the tibia at the right knee joint to those of the left knee joint on T2WI. In addition, we compared statistically the coefficient of variance (CV) of signal intensity on the subchondral bone, the area (mm 2 ), the major axis (mm) and the minor axis (mm) of the upper end of the tibia by the use of micro-CT images. Results: In MRI experiment, the relative signal value was significantly higher at 2, 6, and 10 weeks postoperatively in the medial part of right knee joint than that in the left one. In micro-CT experiment, CV was significantly higher from 6 weeks postoperatively in the subchondral bone of surgical side. Rough and irregular surface at the medial tibia was also observed by 3D images. Conclusion: Using 7 T-MRI and micro-CT, we're able to observe the knee osteoarthritis model rat longitudinally.