Since neovascularization has been reported that it is associated with tendinopathy, assessments of vascularity are important for both diagnosis and treatment estimation. Photoacoustic imaging, taking the advantages of good ultrasonic resolution and high optical absorption contrast, has been shown a promising tool for vascular imaging. In this study, we explore the feasibility of photoacoustic micro-imaging in noninvasive monitoring of microvascular changes in Achilles tendon injuries on a mouse model in vivo. During collagenase-induced tendinitis, a 25-MHz photoacoustic microscope was used to image microvascular changes in Achilles tendons of mice longitudinally up to 23 days. In addition, complementary tissue structural information was revealed by collateral 25-MHz ultrasound microscopy. Morphological changes and proliferation of new blood vessels in Achilles tendons were observed during and after the acute inflammation. Observed microvascular changes during tendinitis were similar to the findings in the literatures. This study demonstrates that photoacoustic imaging can potentially be a complementary tool for high sensitive diagnosis and assessment of treatment performance in tendinopathy.