An online buyback system is provided, including: a database storing product sale information including product identification information, product specification, product sale price, and product, sale date; a buyback request information receiving unit receiving buyback request information including product identification information from a computer of a buyback requester accessing a network; a sale checking unit referring to the product sale information stored in the database to check whether or not a product corresponding to the product identification information contained in the buyback request information has been sold; and a buyback processing unit processing such that the product corresponding to the product identification information is collected from the buyback requester when the product is determined to have been sold, and a buyback price of the product is paid to the buyback requester based on a time interval from the product sale date to buyback request date.