For any given matrix A ∈ C, a preconditioner t(A) called the superoptimal preconditioner was proposed in 1992 by Tyrtyshnikov. It has been shown that t(A) is an efficient preconditioner for solving various structured systems, for instance, Toeplitz-like systems. In this paper, we construct the superoptimal preconditioners for different functions of matrices. Let f be a function of matrices from C to C. For any A ∈ C, one may construct two superoptimal preconditioners for f(A): t(f(A)) and f(t(A)). We establish basic properties of t(f(A)) and f(t(A)) for different functions of matrices. Some numerical tests demonstrate that the proposed preconditioners are very efficient for solving the system f(A)x = b.