  We employ QCD sum rules to calculate the $J/\psi$ form factors and coupling
constants with charmed mesons, by studying three-point correlation functions.
In particular we consider the $J/\psi D^*D$ and $J/\psi DD$ vertices. We
determine the momentum dependence of the form factors for kinematical
conditions where J/\psi, D or D^* are off-shell. Extrapolating to the pole of
each one of the so obtained form factors, we determine the coupling constants.
For both couplings our results (within the errors) are compatible with
estimates based on constituent quark model.
