Synovitis is a driver of osteoarthritis. Imaging of the synovial vasculature is essential for osteoarthritis assessment, while traditional imaging techniques like contrast-enhanced MRI/CT and conventional ultrasonography have limitations such as invasive manipulation, radiation and subjective results. In this study, an emerging non-invasive ultrasound imaging technique – optoacoustic molecular imaging (OA) was applied to evaluate the synovial vasculature in a mouse model of knee joint osteoarthritis. 16 male Balb/c mice undertook destabilization of medial meniscus surgery (DMM), 8 were intact as baseline controls. Three-dimensional high-frequency ultrasonography, including B mode, Power Doppler (PD) and OA, was performed to the knees of live mice at baseline (n=8), 1 month (n=8), and 4 months (n=7) after DMM, before tissue harvest. We found that OA vascular density increased significantly at 1 month (p=0.028) and remained high at 4 months (p=0.541), indicating synovial neovascularization during osteoarthritis progression, which was consistent with uCT-based angiography and histological findings. Meanwhile, OA could also evaluate the function of the synovial vasculature by measuring blood oxygen saturation (sO2). We found OA sO2 declined significantly at 4 months compared to baseline (p=0.043) and 1 month (p=0.027), indicating vascular dysfunction at late stage osteoarthritis. Moreover, OA sO2 was found closely related with histological cartilage damage (p=0.028). In this study, we demonstrated that OA was reliable to evaluate the small vasculatures in the knee joint of DMM mouse model. Our findings provided a new technique for the non-invasive monitoring of both structure and function of the synovial vasculature during osteoarthritis progression.