In this paper we present a fast iterative image superresolution algorithm using preconditioned conjugate gradient method. To avoid explicitly computing the tolerance in the inverse filter based preconditioner scheme,1 a new Wiener filter based preconditioner for the conjugate gradient method is proposed to speed up the convergence. The circulant-block structure of the preconditioner allows efficient implementation using Fast Fourier Transform. Effectiveness of the preconditioner is demonstrated by superresolution results for simulated image sequences.