The present invention relates to a mobile communication system, and more particularly, to a method and system for efficiently supporting security in a mobile communication system. The method for supporting the security of a terminal in a mobile communication system according to the present invention comprises: a process of transmitting an information provision request message to a network; a process of performing a verification for the network and security; a process of receiving an information provision response message, comprising an index of an encrypted security key, an International Mobile Subscriber Identity (IMSI), and a security-related profile from the network when the verification is completed; and a process of selecting a security key on the basis of the index of an encrypted security key, and then storing the selected security key, the IMSI, and the profile.