  We express the action of six-dimensional supergravity in terms of
four-dimensional N=1 superfields, focusing on the moduli dependence of the
action. The gauge invariance of the action in the tensor-vector sector is
realized in a quite nontrivial manner, and it determines the moduli dependence
of the action. The resultant moduli dependence is intricate, especially on the
shape modulus. Our result is reduced to the known superfield actions of
six-dimensional global SUSY theories and of five-dimensional supergravity by
replacing the moduli superfields with their background values and by performing
the dimensional reduction, respectively.
