The present invention relates to a real estate rental fund operating system using internet and an operating method thereof capable of guaranteeing a payback in case a fund contract ends, and guaranteeing the fixed earning rate of the rental profit of a real estate. The real estate rental fund operating system using internet of the present invention according to the present invention includes : a web server of a specific securities company which advertises and/or sells a real estate rental fund product to a general company or a person based on real estate investment information of a real estate having an ownership contract with a developer of a specific real estate which finishes a construction, is under construction, or is planned to be constructed by the specific developer, processes the distribution of rental profits to each investor by a preset contract duration unit, and processes an investment principal, which is returned when the contract duration of the corresponding real estate rental fund ends, in order to be paid to an investor; and at least one user terminal which joins the real estate rental fund through an internet network and selects a subscription option of the real estate rental fund and an expiration option of the real estate rental fund.(100) Web server of a real estate management company(200) Database of a real estate management company(300) Web server of an asset management company(400) Web server of a specific securities company(500) Web server of a specific trust company(600) Developer server(700a, 700n) User terminal(800) Internet networkCOPYRIGHT KIPO 2015