  We present our preliminary results for semileptonic form factors of $D$
mesons in unquenched lattice QCD. Simulations are carried out with $n_f=2+1$
dynamical quarks using gauge configurations generated by the MILC
collaboration. For the valence quarks, we adopt an improved staggered light
quark action and the clover heavy quark action. Our results for $D \to K$ and
$D \to \pi$ form factors at $q^2=0$ are in agreement with the experimental
values.
