This paper examines the boundaries of the internal labor markets in Mitsubishi Zaibatsu and the career paths of the employees of Mitsubishi Bank, using the employee lists of Mitsubishi Zaibatsu. The fact that a comprehensive employee list was compiled by the personal section of the holding company every year, suggests that there might be a unified internal labor market of Mitsubishi Zaibatsu. However, transfers of employees between the affiliated companies were exceptional, which means that the internal labor market in Mitsubishi Zaibatsu was partitioned into the internal labor markets of the individual companies. On the other hand, each of those internal markets was relatively open to the external market, compared with major companies in present Japan. It is also found that the career paths of the employees of Mitsubishi Bank were different from those of the bank employees in present Japan. In particular, many of the loan section chiefs of Mitsubishi Bank did not have much experience as loan officers, while they spent long time in various sections including deposit section and exchange section.