Naturalism was first proposed and formulated by French novelist Emile Zola, and it was introduced to America by American novelist Frank Norris. It is a new and harsher realism. It is a theory in literature emphasizing scientific observation of life without idealism or avoidance of the ugly. American literature naturalists dismissed the validity of comforting moral truths. They attempted to achieve extreme objectivity and frankness, presenting characters of low social and economic classes who were dominated by their environment and heredity. The pessimism and deterministic ideas of naturalism pervaded the works of such writers as Stephen Crane, Frank Norris, Jack London, Henry Adams, Theodore Dreiser, and Hemingway etc. This essay intends to deal with the application of naturalism in American literature and thereby seeks a broader understanding of naturalist literature in general.