A modular form is called a Hecke eigenform if it is a simultaneous eigenvector for the Hecke operators. The Fourier coefficients of a Hecke eigenform are regarded as its eigenvalues (Hecke eigenvalues) and satisfy numerous arithmetic properties. J.-P. Serre gave an algebraic interpretation of Hecke eigenvalues arising from mod p modular forms. We generalize Serre’s result to mod p automorphic forms on Shimura varieties of Hodge type. This is joint work with Chia-Fu Yu.