Some embodiments disclosed herein are a method and a system for displaying an advertisement on a web page in which advertisement data displayed on the same web page from among different advertisement data can check mutual existence of the displayed advertisement data, thereby displaying another advertisement data different from the displayed advertisement data. The method for displaying another advertisement data includes recording and maintaining advertisement data including respective identification numbers in an advertisement database, loading the advertisement data from the advertisement database to a local computer memory of a user connected with a web page, identifying advertisement data having an identification number among the advertisement data loaded to the local computer memory, identifying predetermined option which may comprise predetermined display advertisement data from the advertisement database when the advertisement data having the identification number exists, and displaying the display advertisement data on the web page.