  We investigate observational constraints on the generalized Chaplygin gas
(GCG) model as the unification of dark matter and dark energy from the latest
observational data: the Union SNe Ia data, the observational Hubble data, the
SDSS baryon acoustic peak and the five-year WMAP shift parameter. It is
obtained that the best fit values of the GCG model parameters with their
confidence level are $A_{s}=0.73^{+0.06}_{-0.06}$ ($1\sigma$)
$^{+0.09}_{-0.09}$ $(2\sigma)$, $\alpha=-0.09^{+0.15}_{-0.12}$ ($1\sigma$)
$^{+0.26}_{-0.19}$ $(2\sigma)$. Furthermore in this model, we can see that the
evolution of equation of state (EOS) for dark energy is similar to quiessence,
and its current best-fit value is $w_{0de}=-0.96$ with the $1\sigma$ confidence
level $-0.91\geq w_{0de}\geq-1.00$.
