A method and apparatus for authenticating a user based on an utterance input includes obtaining an input audio signal based on the utterance input of the user; obtaining, from the input audio signal, at least one audio signal of an utterance section and at least one audio signal of a non-utterance section; generating environment information indicating an environment in which the utterance input is received, based on the at least one audio signal of the non-utterance section; obtaining a result of a comparison between the generated environment information and registration environment information indicating an environment in which a registration utterance input corresponding to a previously registered registration audio signal corresponding to the user is received; adjusting an authentication criterion for authenticating the user based on the result of the comparison; and authenticating the user based on the adjusted authentication criterion and the input audio signal.