Major studies on cell production have put the emphasis on technical factors such as machine order / layout,family part grouping, workŽow sequence, etc., it is still insu fficient to investigate how human factors affect the productivity of production cells. Although many companies have introduced cell production systems and realized that productivity of cells varies greatly with workers, there are no reports published on the statistical characteristics and distribution of workers' productivity. In order to assess the impact of workers' aptitude on productivity, we have made a series of experimental studies and questionnaire analyses. In this paper, we summarize the results of our production experiments conducted for four years, show statistical characteristics of workers' productivity, and then conduct cluster analysis to provide some insights to the workers' aptitude toward to cell production. Through these examinations, it is clear that 18.6% of workers have higher aptitude than the majority (53.1%), and there are 22.1% of workers with lower aptitude to cell production. Meanwhile, It can be considered that 6.2% of workers are not suitable to assembly tasks in cell production.