  We study the impact of dimension-six operators on single- and double-Higgs
production rates via gluon fusion at the Large Hadron Collider (LHC). If the
top-Yukawa coupling is modified by some new physics whose scale is of the TeV
scale, its effect changes the cross sections of single-Higgs production $gg\to
H$ and double-Higgs production $gg\to HH$ through the top-loop diagram. In
particular, double-Higgs production can receive significant enhancement from
the effective top-Yukawa coupling and the new dimension-five coupling $t{\bar
t}HH$ which are induced by the dimension-six operator. Comparing these results
to the forthcoming data at the LHC, one can extract information of the
dimension-six operators relevant to the top quark and the Higgs boson.
