On the basis of the scalinp: theory of locallzation, we introduce an effective dimensionality for layered structure systems, which depends on the conductivity anisotropy or the interlayer coupling. We propose that both decrease of conductance and drop in effective dimensionality account for the metal-insulator transitions in YBa2Cu3O7-x and other oxide compounds. The scaling theory in finite temperatures is also discussed to explain the temperature dependence of the normal state resistivities.