This paper titled ‘Language structure and use in the selected plays of Eugene O’Neill’ aims to bring out how Eugene O’Neill’s plays has specific style of expressions in the structure and use of language. His plays are expressionistic plays and they are loose in structure. Expression is composed of a system of words, phrases, sentences which are spoken, heard, felt or imagined independently of their particular meanings. It is varied according to the sociolinguistic contexts and situations. The language structure and use of the selected plays ‘The Hairy Ape’, ‘The Emperor Jones’, and ‘Long Day’s Journey into Night’ consist of expressions which reveals the inner significance of the play through the use of poetic, grammatical, lexical and phonological structures. The same language is used distinctively by the playwright. It shows the significance of the author’s choice of language which is distinct from normal language. It has various forms of language such as slang, colloquial and informal varieties. The language of Negroes called ‘Black English’ is used in ‘The Emperor Jones’. The speech of American Blacks also called ‘Black English’ is used in ‘The Hairy Ape’. This paper also deals with the use of three types of meanings - referential, social and affective and highlights the language power and linguistic personality of Eugene O’Neill. Key Words: structure, language usage, lexical and phonological structures, sociolinguistic contexts and situations,