The objectives of this research were to examine the relationship between the state’s politics and the identity of Thai Song Dam ethnic group, and further, to investigate the identity contestation within the ethnic group in Khao Yoi district, Petchaburi province. The research methodology included documentary and field research with in-depth interviewsalong with participatory and non-participatory observations. The research results revealed that it is indeed critical to understand the relationship between the majority group (Thai people) who governed the minority group of Thai Song Dam. The state policies before and after 1932 have significantly affected the ethnic identity of this particularly minority group, both voluntary and involuntary. The identity contestation within the ethnic group revealed that there was a disagreement in regard to the definition of ‘true Thai Song Dam’, as the current identity is one that has been shaped and assimilated. As a consequence, the ethnic group has attempted to explore the ground of their identity by expressing themselves in various forms.