Abstract: We investigated the topological structure of approximation operators satisfied reflexive and transitive rela- dons on the universe which is not restricted to be finit. It was proved that there is a oncto-one correspondence between the set of all reflexive and transitive relations and the set of all topologies. It gave the base of topological space.

Key words: Rough set, Topology, Approximation operator, Reflexive relation, I}ransitivc relation