  We present an $S_4$ flavor model to unify quarks and leptons in the framework
of the SU(5) GUT. Three generations of $\bar 5$-plets in SU(5) are assigned
$3_1$ of $S_4$ while the first and the second generations of 10-plets in SU(5)
are assigned to be 2 of $S_4$, and the third generation of 10-plet is to be
$1_1$ of $S_4$. Right-handed neutrinos are also assigned 2 for the first and
second generations and $1_1$ for the third generation, respectively. Taking
vacuum alignments of relevant gauge singlet scalars, we predict the quark
mixing as well as the tri-bimaximal mixing of neutrino flavors. Especially, the
Cabbibo angle is predicted to be $15^{\circ}$ in the limit of the vacuum
alignment. We can improve the model to predict observed CKM mixing angles.
