Ethnic identity which Athens used has three functions: One is to integrate those who has the same belief that they are the Ionians. Two is to eliminate those who are non Ionians. Three is to justify the policy of Athenian colonization as the metropolis of the Ionians. These three functions are called here "ethnic ideology". However it is necessary to notice that the ethnic identity is an imagined belief created by somebody on purpose with a great effort. The purpose of this paper is to overlook how the Athenians the ethnic ideology for her colonization had used from 561 to 338 B.C. The outcome of this discussion also would provide us with a key to solve a so-called Apoikia -Klerouchia problem. The outline of this paper is as follows: (1) Time of Peisistratos: According to the strategies of the factional leaders in Attica, there were two main streams of Athenian colonization. The one is the north Aegean colonization. The other is the around Attica colonization. All the colonies in this time were lost by the Persian Wars except for Salamis, which is the first case that the ethnic ideology was introduced into. (2) Time of Cimon: Cimon, who was born in the Chersonese as a son between Miltiades and a daughter of Oloros the king of Thracia, sought to recover the north Aegean colonies not only for Athens out also rather for himself. Thucydides, who is a kinsman of Cimon's family, suggested that the ostensible cause of the establishment of the Delian League was to fight against the Persians. (3) Time of Pericles: In his time a great number of Athenian colonies were founded. The two patterns of conization were clearly seen. The one is a colony founded by expelling non Ionic residents, the other is by sending colonists into Ionic residents. (4) Time of Cleon: The plaque changed the situation. Loss of population and deterioration of moral made her colonization more serious. It was almost only one pattern to execute all the non Ionic residents and to sell their wives and children as slave. Athens, however, could not send out their colonists. (5) Time of Timotheos: By the end of the Peloponnesian War, almost all of the Athenian colonies were again lost. Therefore the main problem of Athens of this century was to recover the lost colonies. Athens, however, was no longer strong enough to achieve this purpose. Athens obviously gave up the ethnic ideology. They could maintain her overseas territories only by a recognition of the Persian King. Therefore the Athenians should have claimed that the territories were indispensable part of Attica where the Athenian citizens lived.