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 .