This paper attempts to concentrate on the often-neglected character Nick in The Great Gatsby from the aspect of his structural and thematic roles in the novel. Nick is confronted with the struggle of two kinds of moral values. His attitude is shifted from the tolerance for the rich and contempt for Gatsby to the contempt for the rich and sympathy for Gatsby. Fitzgerald makes Nick to play the significant role among all leading actors, the link in the structure and the revealer of the theme.