Empirical study of language and ethnic identity interrelations in Khazakhs residing in poli-ethnical region is presented. It has been found that the level of competence in ethnic and "foreign" language and the degree of its coincidence with verbal behaviour influence contents and manifestation of ethnic identity. High competence in native language and low one in foreign (Russian) language result in mono-ethnical identity accompanied by marked inter-group favouritism. Equal competence in ethnic and "foreign" languages promotes biethnical competence and biethnical identity formation. Language assimilation in ethno-social situation characterised by ethnic language prevailing results in interpersonal conflicts and marginal ethnic identity formation.