Summary: S-boxes bring the only nonlinearity to symmetric ciphers and strengthen their cryptographic security. A detailed analysis of the cryptographic properties of S-boxes in several symmetric ciphers, such as AES, SEED, Camellia and SMS4, is made in this paper. The algebraic properties and the Boolean functions of S-boxes are well investigated. Then the attack capabilities resisting to differential cryptanalysis and linear cryptanalysis are provided. At last, the securities of AES, SEED, Camellia and SMS4 are revealed by comparing the advantages and disadvantages of the S-boxes used in these symmetric ciphers.