Abstract: Legitimacy theory receives many researchers’ attention in the fields of political science and organizational science. Both of them came from the social value and norm in Greek philosophy. However， the two theories went down their independent ways from the time of Max Weber’ theory related to political legitimacy at the beginning of last century， and then founded the political legitimacy theory (PLT) and organizational legitimacy theory (OLT) on their own. Now in China， there are much more PLT research in present literature and much less research about OLT. So it is important to compare the two theories and find the differences between them to help Chinese scholars to understand the theories and put them into use.