  $J/\psi$ production has been measured in Au+Au and Cu+Cu collisions at
$\sqrt{s_{NN}}$ = 200 GeV by the PHENIX experiment at the Relativistic Heavy
Ion Collider (RHIC) during 2004 and 2005, respectively, at mid-rapidity
($|\eta| \le$ 0.35) via $J/\psi$ $\to$ $e^{+}e^{-}$ decay and at forward
rapidity (1.2 $\le | \eta | \le$ 2.2) via $J/\psi$ $\to$ $\mu^{+}\mu^{-}$
decay. The nuclear modification factor ($R_{AA}$) of $J/\psi$ is presented as a
function of the collision centrality for Au+Au collisions (final results) and
Cu+Cu collisions (preliminary results) in both rapidity windows. These results
are compared to SPS results at lower energy and to various theoretical
calculations.
