MDS Matrix has an important role in the design of Rijndael Cipher and is the most expensive component of the cipher. It is also used as a perfect diffusion primitive in some other block ciphers. In this paper, we propose a replacement of Mix Column Transformation in AES by equivalent Dynamic Mix Column Transformation. A Dynamic Mix Column Transformation comprises dynamic MDS Matrices which are based on default MDS Matrix of AES and mbit additional key. Here m is a variable length that does not exceed the product of