This paper intends to study a trilogy of U. S. A. of John Dos Passos, one of the most neglected writers in the modern American novel. Writing his major works in the 1920s and 1930s, Dos Passos represents both modernism and leftism in American literature. While critics has traditionally regarded modernist literature and leftist literature as opposed to each other, Dos Passos`s trilogy, The 42nd Parallel, 1919, and The Big Money, is remarkable for showing how those two literary attempts can coexist. Interestingly, he juxtaposes modernist literary experiment with leftist critiques of capitalist America of the first three decades of the 20th century to negotiate them within a context of American experience. This paper concretely examines how Dos Passos employs literary modernism and leftism and negotiates or, as it were, `Americanizes` them in U. S. A. The modernist elements are remarkable in the formal experiments of the trilogy. The narrative structure of U. S. A. consists of four different layers, such as Newsreel, Biography, Narrative, and Camera Eye. Dos Passos presents a panorama of various experience of modern America through the multi-layered narratives interrelated to one another both thematically and structurally. In addition, a diversity of narrative techniques, from Camera Eye`s impressionist stream- of-consciousness to the naturalist documentary in Newsreel and the objective narratives of major characters, enrich the prose style of the trilogy, while multiple kinds of American language vividly deliver the polyphonic voices of America. Within this narrative structure, Dos Passos critically analyzes the social and economic reality of America from the class-conscious and materialist perspectives of leftist literature. This leftist analysis attacks the systematic evils of capitalist America, such as the collapse of democratic ideals, mechanization of labor, monopoly capitalism, and the corruption of American Dream. And the narrator of Camera Eye, who gradually grows into a serious radical toward the end of the trilogy, harshly condemns America for its betrayal of the founding fathers` spirit of liberal democracy that culminates in the Sacco-Banzetti case. U. S. A. reveals American characteristics in blending those modernist and leftist elements. The mass culture of America is actively incorporated in the modernist innovation of the novel form, while the formal experiment effectively contributes to a critique of the mechanized American society. But Dos Passos`s American negotiation discloses some problems in its nostalgic compromise with a Jeffersonian past of liberal democracy. Without any critical insight into its dark history, Dos Passos idealizes American democracy as the only alternative to reality.