Musculoskeletal (MSK) ultrasonography enables us not only to perform structural evaluation of various musculoskeletal tissues but also to perform a dynamic assessment. In this report, we present some cases in which MSK ultrasonography was efficiently employed in the dynamic assessment. In the field of rehabilitation, physiotherapy in particular, evaluation of subjects mainly depends upon the therapist's inspection, palpation, and experience. MSK ultrasonography is a new and effective tool that makes evaluation of subjects more accurate and effective. It serves in the evaluation of muscle strength training, and assesses various risks by identifying structures such as vessels and nerves and/or motion. It also gives both the therapist and patient visual feedback, providing information on the MSK system easily and noninvasively, in comparison to electromyography and traditional imaging modalities such as X-ray, CT, and MRI. Despite its ease of use and noninvasiveness, MSK ultrasonography is in general regarded as an operator-dependent imaging modality, which indicates it inherently has a problem in terms of reproducibility. Therefore, in the present report, we introduce ultrasonographic techniques that have been validated in previous reports in the literature. We focused on the clinical application of MSK ultrasound in the treatment of quadriceps and core muscles, which are common problems in the field of rehabilitation, and also discussed the importance of MSK ultrasonography in the rehabilitation of the lumbar spine and medial patellofemoral ligament.