  The effect of massive neutrinos on matter power spectrum is discussed in the
context of $f(R)$ gravity. It is shown that the anomalous growth of density
fluctuations on small scales due to the scalaron force can be compensated by
free streaming of neutrinos. As a result, models which predict observable
deviation of the equation-of-state parameter $w_\DE$ from $w_\DE=-1$ can be
reconciled with observations of matter clustering if the total neutrino mass is
$O(0.5 \eV)$.
