Realism was a very important movement in the history of American drama, which during 1913—1933experienced its cutting-edge period thanks to Eugene O’Neill’s contribution. This paper deals with O’Neill’s dramatic realism through two angles, the comprehensive background of his realism and the characteristics of his dramatic realism. Through analyzing Long Day’s Journey into Night, the author endeavors to offer a better understanding of his realism. Literary realism is commonly defined as “a mode of writing that gives the impression of recording or reflecting faithfully an actual way of life” (Baldick 184). This explicit definition presents nothing more or less than a general quality that realistic works takes on, and serves as a commonly recognized pattern that realistic writers follow in their literary works. Baldick regards it as “an actual way of life” (Baldick 184), which is the most important element. Although Eugene O’Neill was generally recognized as the best dramatist in American history, he was consistently experiencing in rejuvenating the drama of the 19th century tradition and employing realism and naturalism into his play. “O’Neill’s ceaseless experimentation enriched American drama and influenced later playwrights as Tennessee Williams, William Inge, and Edward Albee. It is possible that he will go down in the history of American drama as the American Shakespeare” (Chang 368). O’Neill with his 49 plays (published) called forth the advent of a brand new era—American Dramatic realism. Realism was a very important movement in the history of American drama, which during 1913-1933experienced its cutting-edge period thanks to Eugene O’Neill’s contribution. This paper deals with O’Neill’s dramatic realism through two angles, the comprehensive background of his realism and the characteristics of his dramatic realism. Through analyzing Long Day’s Journey into Night, the author endeavors to offer a more understanding of his realism. Literary realism is commonly defined as “a mode of writing that gives the impression of recording or reflecting faithfully an actual way of life ”(Baldick 184). This explicit definition presents nothing more or less than a general quality that realistic works takes on, and serves as a as generally known pattern that realistic writers follow in their literary works. Baldick regards it as “an actual way of life” (Baldick 184), which is the most important element. Although Eugene O’Neill was generally recognized as the best drah matist in American history, he was consistently experiencing in rejuvenating the drama of the 19th century tradition and employing realism and naturalism into his play. “O’Neill’s ceaseless experimentation enriched American drama and influenced later playwrights as Tennessee Williams, William Inge, and Edward Albee. It is possible that he will go down in the history of American drama as the American Shakespeare ”(Chang 368). O’Neill with his 49 plays (published) called forth the advent of a brand new era-American Dramatic realism .