After the DES (Data Encryption Standart) algorithm was unreliable, a content was held in September 1997 by the US National Institude of Standards and Technology (NIST) to designate a cryptographic algorithm for national civilian use. After four years of evaluation and elimination, the results were announced in October 2000 and announced to be used as the Advanced Encryption Standard (AES) of the Rijndael Algorithm, designed by NIST, Joan Daemen and Vincent Rijmen. The relevant standard was announced by the US National Institute of Standards and Technology (NIST) in November 2001 with the US FIBS PUB 197 coded document. In this study, the encryption process is investigated with 128 bit Rjindael Algorithm which is determined as AES.