An apparatus and method for authenticating a telematics terminal are disclosed to receive a first telematics service based on inputted user authentication information and then easily receive a second telematics service based on the inputted user authentication information. The method for authenticating a telematics terminal in a vehicle including: storing user authentication information inputted to receive a first telematics service through a mobile communication network; and requesting a second telematics service to an information providing center through the mobile communication network based on the stored user authentication information.