The tensile mechanical behaviour of quenched and annealed isotactic polypropylene (iPP) films has been analysed over a wide range of strain rates, i.e. from 10(-3) to 3 x10(+2) s(-1). Evolution of mechanical properties of such films versus strain rate has been analysed through the microstructure. Thus, both the Young’s modulus and the yield stress could be mainly controlled not only by the crystallinity ratio but also by the physical cross-linking degree of the amorphous phase induced by crystal line entities. For a given crystallinity ratio, the drawability of quenched and annealed iPP films is mainly controlled by the sum of the effects induced by both the physical cross-linking degree of the amorphous phase and the perfection degree of the crystalline phase. The increase in annealing temperature leads to the opposite evolution of these two microstructural parameters and then to opposite effects on the drawability of fiIms. Changes in original microstructure of quenched films induced by drawing at various draw ratios and at various strain rates are also discussed.