Disclosed are a server, a system, and a method to provide information for a real estate transaction. The online real estate information providing system includes : a server which provides an online real estate information providing website; and at least one seller terminal, at least one purchaser terminal, and at least one intermediary terminal which access the server through a wired and wireless communication means. The online real estate information providing method, as an online real estate information trading method, includes the steps of : respectively inputting selling information and purchase information into the seller terminal and the purchaser terminal through the website; combining the selling and purchase information from the server to calculate a possibility of achieving a transaction as possibility information and displaying the possibility information on the website; searching interest information in the intermediary terminal based on the displayed possibility information and inputting a bidding request information, which includes a bidding price, in the interest information; determining an intermediary for a successful bid according to predetermined standards by analyzing inputted bidding request data in the server after a predetermined time period; requesting the intermediary for a successful bid to pay the bidding price as deposit money of an achieved transaction of the interest information in the server; and providing the selling information and the purchase information, related to the interest information, to the intermediary for a successful bid if the completion of the payment is confirmed within the predetermined period in the server. Therefore, the present invention enables a transaction to be performed under reasonable transaction conditions, is able to form the proper price of a real estate, and enables a rapid real estate transaction by making a seller and a purchaser actively provide information and providing reproduced information at a possibility for a transaction achievement by combining the selling information with the purchase information.(100) Server(200-1, 200-2, 200-N) Seller terminal(300-1, 300-2, 300-N) Purchaser terminal(400-1, 400-2, 400-N) Intermediary terminalCOPYRIGHT KIPO 2015