We present the electrical properties of polycrystallineLa0.7−xPrxSr0.3MnO3in which the average ionic radius of the A site⟨rA⟩is systematically varied while keeping the carrier concentration fixed. Below the Curie temperatureTc,the spin-disorder scattering process has been regarded to play an important role in the resistivity. With decreasing⟨rA⟩,the structure transition from rhombohedral to orthorhombic phase accompanied with the sharp increase in resistivity atTcand the increase of the activation energies has been observed. ©1997 American Institute of Physics.