Although the tasks are being mechanized or automated today, many tasks are still performed manually in several industrial settings. Manual materials handling and improper sorking postures are known to be a major cause of low back injuries, which are one of the major problems in the economic and public health aspects. In this study, two machine repair shops of a manufacturing company in Pohang were recommended by the company health care center to investigate the potential risk factors that may cause low back injuries. Five machine repair tasks were selected from each machine repair shop, which are accountable for relatively high complaints of low back pain. The purpose of this study is to quantitatively evaluate the hazards of the tasks, and finally to recommend the improved methods and guidelines for safe work practices. In order to accomplish this goal, the questionnaire study and ergonomic evaluations were carried out and the results were analyzed. For most of the tasks under study, workers were found to be exposed to relatively high biomechanical stresses in low back, mainly due to the heaby objects handled and the improper working postures.