  We consider the non-Gaussianity of the nonlinear density perturbations in a
single-field inflationary model when a scalar field couples nonminimally with
gravity. Gravity theories with a nonminimal coupling can be transformed into
the Einstein gravity with canonical kinetic terms by using a suitable conformal
transformation. We find that a nonlinear generalization of the gauge invariant
quantity $\zeta_i$ is invariant under the conformal transformation. With the
help of this conformal invariant property, we calculate the non-Gaussianity,
which is characterized by a nonlinear parameter $f_{NL}$, in nonminimal coupled
scalar field theory.
