An apparatus and a method for performing encryption or decryption of data in a portable terminal, which performs an encryption or decryption operation from a point where the encryption or decryption operation is not generated when power is turned off and then turned on during the encryption or decryption operation, are provided. The apparatus includes a file system analyzer for extracting information of a data block, in which actual user data is stored, through metadata of a file system, and generating a data block list, and a journaling manager for storing a data block corresponding to the data block list among data blocks stored in a memory in a journaling storage unit, and deleting the data block stored in the journaling storage unit when an encryption or decryption operation for the data block stored in the journaling storage unit is completed.