A method for performing transaction with an instant message in an information input window is provided to minimize burden of a buyer requesting communication to a seller when the buyer wants to buy goods through real-time messaging, and enable the buyer to contact with the sellers directly and easily by using a trade name or a unique name of a seller. A database stores seller information including goods name information and an IM(Instant Messenger) ID of a seller. A sender transmits a message to a system by inputting a goods name and purchase inquiry information to an information input window. The goods name and the purchase inquiry information are recognized from input expression, and the seller information corresponding to the goods information is extracted by referring to the database(302). The recognized purchase inquiry information is transmitted to the IM ID of more than one seller corresponding to the extracted seller information by using an instant message form(305). The seller starts a business talk by sending a response to the buyer through an IM(306).