Work of physical labor is conducted in many parts of different workplace. The relationships between a poorly designed workplace, poor working posture and diseases of the musculoskeletal system have been demonstrated. A number of studies also have reported that cleaners have a high risk of developing health problems particularly musculoskeletal problems, especially affecting the back, neck, shoulders, elbows and hands. This study used task analysis to analyze the typical cleaning job and used OWAS to analyze the working postures of cleaning workers in the university environment. We collect the all daily routine cleaning tasks for task analysis. Thirty cleaning workers, with an average work experience of 8.5 years, participated in this study. For an overall distribution of trunk postures, OWAS identified that a bent and twisted trunk posture, which fell into action category 3, was the major poor posture for cleaning workers. Distribution of arm posture were also fell into action category 3. This study also identified that trash cleaning task, class washing task, and toilet cleaning task were the 3 principal tasks in which cleaners cleaning the school environment exhibited poor working posture. This study used the posture analysis of OWAS to redesign the assistant cleaning tools. We extend the length of tools by the heights of the cleaners and the angle of cleaning tool could be adjusted by the different tasks of cleaning job. The redesign tool would help the cleaners to work without the over extending postures. To help them work with the normal postures to reduce and evaluate poor posture in a dynamic cleaning job site.