For centuries ancient Greeks sent many overseas colonies to extend incessantly their world. It is clear that the colonial activity was one of their basical ways of life. With this in view, the kleroukhia, a peculiar type of the Athenian colonies, that flourished especially in the fifth century, should be considered under the light of the contemporary political development of Athens. The present paper surveys every evidence concerning the problem of kleroukhia, referring to the discussions of Ehrenberg, Blunt, Graham and others about it. The following two themes are treated in detail: At first, what were the differences between the kleroukhia and other types of the contemporary Athenian colonies ? After all the theory must be maintained that kleroukhoi were the only colonists with full Athenian citizenship. Next, what did the kleroukhia for Athens ? Answering this would lead us to a better understanding of the Periclean politics.