A method and system of providing a Social Network Service (SNS) interlocking with a phone book of a portable terminal are provided. The method includes searching for an item that corresponds to subscriber information of the SNS, extracting information that corresponds to the searched item from the phone book of the portable terminal, converting the information into a specified data format, transmitting the information to an SNS server, searching for values that coincide with the received information converted into the specified data format, converting the searched values and corresponding SNS IDs into the specified data format, and transmitting the converted values and the corresponding SNS IDs to the portable terminal.