The present invention relates to a system to provide a real estate agency service and a method thereof, capable of enabling users, who want to buy or sell a property through the Internet, to conveniently negotiate and trade with a plurality of traders over prices and trade conditions on the Internet. According to the present invention, the system includes : an application for a seller terminal, registering a property for sales by inputting sales conditions including a sales price; an application for a purchaser terminal, participating in bidding by suggesting a desired bid price for the property registered through the application for a seller terminal; and an agency service providing server linked with each of the applications, opening the bidding of the corresponding property when receiving sales conditions from the application for the seller terminal, and receiving the desired bid price from the application for the purchaser terminal to conduct real estate mediation between the seller and the purchaser through an online bidding method during an opened bidding period.(110) Membership part (seller, buyer, agent)(120) Property registering part(130) Agent verifying part(140) Property bidding part(150) Property search part(160) Bidding participation part(170) Trade contracting part(182) < Real estate information DB> - complex information - property information - actual price information(184) < Sale information DB> - all sale information - by seller(186) < purchase information DB> - all sale information - by buyer(200) Seller terminal APP.(300) Agent terminal APP.(400) Buyer terminal APP.(AA) Selling condition(BB) Purchase conditionCOPYRIGHT KIPO 2018