Neutrosophy has been introduced by Smarandache as a new branch of philosophy. The purpose of this paper is to construct a new set theory called the neutrosophic set. After given the fundamental definitions of neutrosophic set operations, we obtain several properties, and discussed the relationship between neutrosophic sets and others. Finally, we extend the concepts of fuzzy topological space and intuitionistic fuzzy topological spaceto the case of neutrosophic sets.