Substitution box plays an important role in the block cipher algorithm. It can be used to encrypt and decrypt a key in a block cipher. Weaknesses in the substitution box (S-box) can lead to a cryptosystem which is easily broken. A key dependent S-box is needed to make cryptanalysis attacks are difficult to discover a key in a block cipher. In this paper, a key dependent S-box approach is reviewed to improve the security of a cryptosystem. The study found that, a key dependent S-box in a block cipher is more secure and efficient compare than the static S-box. With key-dependent S-box, attacker does not know what the S-box are used and make the system immune to linear and differential cryptanalysis. As a result, a new approach of key dependent S-box is enhanced to produce secure block cipher.