  The Modified Chaplygin Gas (MCG) model belongs to the class of a unified
models of dark energy (DE) and dark matter (DM). It is characterized by an
equation of state (EoS) $p_c = B\rho - A/\rho^{\alpha}$, where the case $B=0$
corresponds to the Generalized Chaplygin Gas (GCG) model. Using a perturbative
analysis and power spectrum observational data we show that the MCG model is
not a sucessful candidate for the cosmic medium unless $B=0$. In this case, it
reduces to the usual GCG model.
