The increase use of computer and communication system by industry and organizations has increased the risk of theft of proprietary information. Although these threats require a variety of countermeasure, encryption process is a primary method of protecting valuable electronic information. The encryption process also needs to be dynamic in order to face new technique and more advance methods used by cryptanalysis. Substitution box (Sbox) is keystone of modern symmetric cryptosystem .They bring nonlinearity to cryptosystem and strengthen their cryptographic security. In this paper RC4 algorithm which is well known stream cipher is used to generate S-box for advance encryption standard (AES). The generated S-boxes are more dynamic and key dependant which will increase the complexity and also make the differential and linear cryptanalysis (DC&LC) more difficult. Various randomness tests are applied to the customized AES (AES-RC4) algorithm and the results shown that the new design pass all tests which proven its security.