The present research paper has been attempted to explore the last phase of Eugene O’Neill. He started his career and expressed his talent with one-act plays. After One-Act plays his career can be divided into three phases. In the first phase 'The Naturalistic and Realistic phase' he used naturalism in his dramatic creations. In the next phase 'the Expressionistic Symbolic phase' he wrote plays of psychological study expressing man's loss of earlier identity with soul or belongingness of faith in religious or social institutions. In the last phase, he again wrote on realism but included it with auto-biographical and psycho-realism in Ah, Wilderness!, Morning Becomes Electra, Long Day’s Journey Into Night, and A Moon for the Misbegotten. The plays of this period can be put under two separate parts of realism—the psychological realism and autobiographical realism. Mourning Becomes Electra and the cycle plays can be put under psychological realism and the last two plays under autobiographical realism.