Background and Purpose: Recently, the Academy of Neurologic Physical Therapy in America has promoted developing movement system diagnosis (MSD). It is because that medical diagnosis is insufficient to guide physical therapy intervention. To establish MSD, standardized examination is needed. Standardized examination includes tests for specific impairments and observational analysis of critical tasks. The aim of this case report is to use observational analysis in designing intervention methods. Methods: The case is a 75-year-old male with acute ischemic stroke. The task chosen in observational analysis was based on the motor function of the case. Movement continuum was used in observational analysis, including initial condition, preparation, initiation, execution, and termination. Intervention was designed according to the problem found in observational analysis. Results: The case is an acute ischemic stroke with left hemiparesis. He could maintain sitting position 2 weeks after onset, but he still could not sit to stand independently. Therefore, sit to stand was chosen as observational task. At initial condition, he sat on the therapeutic mat with hands on the mat and feet on the floor. During initiation, he inclined his trunk slightly. During execution, he tried to extend his legs without buttocks lift-off. During termination, he fell backward and was failed to standup. According to observational analysis, the case lacked forward and upward weight transfer, and he lacked hip extension during execution. The timing to lift the buttock of the mat could be a problem. Hence, the intervention should include weight transfer and hip extension training. Conclusion: Observational movement analysis is convenient to apply in clinical settings, and the results can directly use in task training. Clinical Relevance: Observational analysis is an essential part of MSD and it can apply in movement control and learning.