The work posture impose additional stress upon human workers so that it should be carefully considered in designing works. However, we have a lot of manufacturing plants which convert their standing workplace to sedentary one. To confirm the validity of that trend, the authors conducted an experimental study, and compared the results. The results of the EMG and the self-cognitive symptoms, in general, showed a correspondent trend that the sedentary work posture was rated more comfortable. At the beginning of the work, complaint of the lowerback was higher whereas that of the lower leg and the feet went higher as the time elapsed. If the weight of workpiece were heavier than 500g, increasing rate of bodily discomfort in the sedentary posture were greater than that of the standing posture. In the meanwhile, the standing posture was consistently superior to the sedentary posture in its performance. Thus, in conclusion, for a light assembly work, sedentary work posture would be recommendable because bodily discomfort would be larger irrespective of the small increase of performance increase.