The melt rheological properties of several isotactic copolymers of propylene with either 1-hexene or 1-octadecene, synthesized by the Me2Si[2-Me-Ind]2ZrCl2/MAO catalytic system, are studied under small-amplitude oscillatory shear conditions. Our results show that the addition of short-chain branching (C4 or C16) modifies the main melt properties. The zero-shear-rate viscosity is strongly decreased when the comonomers are incorporated as compared with an equivalent homopolymer of the same molar mass. These experimental findings are in agreement with previous models based on the reptation theory. The plateau modulus and the reptation relaxation time are also decreased with the presence of comonomer. An increase in the activation energy of flow is observed in the polypropylene melt when short-chain branching are incorporated. The changes in the properties depend strongly on the size of the comonomer.