The purpose of this study is to examine the ethnicity of Kayin by the era and identify the people who can be classified as Kayin, nowadays. Specifically speaking, this study aims to review how the ethnicity of Kayin has been socially used in the relation between British colonial government and Burma, in accordance with the each era of the history of Myanmar (from dynasty era to modern times), and its results today. Kayin's ethnic identity was formed through a complex social and historical process. When we think of Kayin, we come up with political ideology group, like 'KNU', which was formed since the independence of Myanmar; and focus on the religious characteristics that they consist of the Christianity. The identify of Kayin, that refused to participate in the federal system; requested for the construction of an independent Kayin's focused on Kayin 'people'; succeeded in militarization, has been often recognized limited to KNU and Christian. However, in fact, Kayin consists of various sub-groups as well as political ideology group like KNU's Christian members. Their residential areas is diverse throughout the entire area of Myanmar, and there are huge differences in the tradition of material living, such as language, religion, food, clothing and shelter; and cultural difference like living economy, among themselves. Kayin's residential quarters are widely scattered and the exercise of powers focused on Burma made the movement of Kayin's the population frequently. Due to frequent population movements, Kayin had to face social and cultural environment and the new relationship with other tribes, when they settled down in the new places. It had the effect on the formation of Kayin's ethnic identity and its changes. Such frequent population movements became the obstacles for Kayin to establish their own population area. Thus, It was almost impossible for Kayin to acquire the land, so that they could exercise autonomy, based on Kayin's ethnicity. The majority of Kayin are still in the economic underclass. Most of them are engaged in small-scale hawking, simple manual works, driving and cleaning; living relatively underdeveloped life. Thus, having a status of Kayin, symbolizes poverty, cultural backwardness, and educational backwardness. So Kayin do not seem to need to acquire Kayin's status. In case of Kayin, dwelling in central/southern area, they frequently come into contact with Burma through active economic activities, and they almost lost their identity, when the structural confrontation is removed and there is no cultural difference. However, Kayin, dwelling in the south eastern area where they had to acutely confronted, still have their identity. However, they are facing the situation in which they have to seek a new way to survive, because the structural confrontation is over, and they are having dual form of ethnic identity. They acquired the identity of Kayin and other tribes(mainly Burma) at the same time, and optionally selected their status. On the other hand, in case of Kayin in the norther area where there was no available transportation with other tribes, many of them recognize their ethnicity as new ethnicity which are totally different from their ethnicity. Especially, self-administered districts have been recently granted to Pao; and they are classified as different ethnic group from Kayin. Thus, today, Kayin has almost perished and only small number of Kayin barely keep their name.