When isotactic polypropylene is quenched at 0 degrees C from the molten state, a biphasic material, amorphous-smectic, is obtained. The smectic phase has an intermediate order between the amorphous and the crystalline. In this study the intrinsic birefringence of the smectic phase was determined. Tapes with different draw ratio were prepared at room temperature, at which the smectic phase does not transform into the crystalline phase. The amount of the smectic phase was determined with measurements of density and sorption of vapors of dichloromethane. The value of the intrinsic birefringence for the smectic phase is : Delta degrees n(sm) = 40 . 10(-3). This value is in good agreement with the values proposed by Samuels for the intrinsic birefringence of the amorphous and the crystalline phases.