Data Encryption Standard (DES) is an encryption algorithm which is primarily used in applications where block cipher mode of operation is required. It is further modified as Double DES (2DES), Triple DES (3DES) in order to provide added security due to extra key length. DES is susceptible to brute force attack and 2DES for meet in middle attack. In this paper we implement a modified DES algorithm in Cipher Block Chaining mode of operation in which key generation procedure differs by using a 112 bit key and the plain text is encoded using a modified playfair technique as input to DES encryption function. Variations in the avalanche affect are observed in the results. Experimental results exhibit a higher avalanche effect in 60% of the cases using the modified DES algorithm.