The greatest American writer Eugene O'Neill (1888- 1953) achieved a recognizable place among the English and American dramatists through the stylistic features of his dramatic language. This study investigates O'Neill's way of handling dramatic language, in Hairy Ape,( the use of grammar from the settled norms in play writing). It endeavors to show how O'Neill manipulates his character's dialogue and the effects of this manipulation.The problem is related to what extent O'Neill's use of language deviates from the linguistic norm, and the levels of linguistic deviation in his style. The study aims to analyze the types of grammatical deviation in O'Neill's 'Hairy Ape'. Moreover, it attempts to justify the reasons behind these deviations (and to support some critical points of view concerning O'Neill's and style in using grammatical deviations).. Deviation as a linguistic phenomenon has an important effect on the readers (and hearers ), if a part of a poem is deviant it becomes especially, noticeable, or perceptually prominent ( Short, 1969: 11 ). Out of the stylistic analysis,it has been found out that the writer uses a language deviated from the literary convention or everyday speech(norm). He uses different types of linguistic deviations to achieve his purposes.