  We investigate whether the final state interaction (FSI) effect plays a
significant role in the large hidden charm decay width of X(3872) and Y(3940)
using a model. Our numerical result suggests (1) the FSI contribution to
$X(3872)\to J/\psi\rho $ is tiny; (2) $\Gamma[ Y(3940)\to
D\bar{D}^{*}+\text{h.c.}\to J/\psi\omega ]$ from FSI is around several keV, far
less than Belle's experimental value 7 MeV.
