It has been very important to have an exact evaluation for risk factors in order to prevent WMSDs(Work-related Musculoskeletal Disorders). However, most WMSDs evaluation methods have always been some problems of possibilities associated with subjective evaluation. Therefore, this study tried to conduct a sort of usability analysis on three major evaluation methods(OWAS, RULA, REBA). Specifically, major subjects in the study consisted of three parts as follows; comparison of the results between experienced and inexperienced observers, analysis for the consistency of the results in terms of different evaluation times, and analysis for the consistency of the results in terms of different job characteristics(based on the part of the automobile). The results of the study were summarized as follows; 1) There was statistically significant difference of the results by RULA and by REBA between experienced and inexperienced observers. This might be due to the fact that experienced observers have had better ability to detect the important working posture during evaluation. However, the results by OWAS did not give any significantly different results between experienced and inexperienced observers, 2) All three checklists applied by experienced subjects did not show any single result significantly different in terms of different evaluation times. This might have to do with high intra-observer reliability from some of previous studies, 3) The five parts of an automobile were selected as five major jobs with different job characteristics in the automobile industry. Specifically, they were door part, front part(hood, etc.), inside part(dash board, seats, etc.), rear part(trunk etc.), and bottom part. All three methods did not show any significant differences for the results from each observers. Further study on this subject would eventually provide a sophisticated evaluating guidelines for WMSDs regarding determination of observer-specific evaluation, identification of repetitive number of evaluations for stable results for each checklist, determination of job-specific evaluation methods, and so on.