The purpose of this paper is to investigate risk factors and ergonomically improve the manufacturing lines of compressors for prevention of work-related musculoskeletal disorders, enhancement of productivity, and workers satisfaction We executed questionnaire survey, ergonomic risk factors investigation of manufacturing lines and ergonomic intervention of work methods, workplace and hand tools. The results of the questionnaire showed that $7.9\%$ of respondents were positive in WMSDs symptom survey. In ergonomic evaluation, the analysis methods such as RULA and NIOSH lifting equation were used and 28 processes in the lines were evaluated to be potentially hazardous. We ergonomically improved the processes to reduce potential WMSDs hazards : manual material handling, carts, work tables, transport methods, working posture and hand tools.