On-line ultrasonic measurements were taken on La0.7Sr0.3CuxMn1−xO3 polycrystalline perovskite materials (with x = 0.05, 0.10, and 0.15), which were prepared using the solid-state reaction technique. X-ray diffraction patterns of the samples confirmed the rhombohedral structure with R3c space group. The obtained X-ray spectra from the energy-dispersive analysis confirmed the elemental composition of the prepared samples. Scanning electron microscopy was used to determine the size of the particles in the samples. The substitution of copper in the Mn site was found to affect the Mn3+/Mn4+ ratio and the density of the charge carriers. The substitution caused an additional disorder that weakened the double-exchange (DE) interaction and reduced the ferromagnetic order. The temperature dependence of the elastic constants derived from the ultrasonic velocities revealed interesting features in the samples. The elastic constants indicated a short-range ferromagnetic to paramagnetic transition at temperatures (TC) of 358, 341 and 328 K for the samples with compositions (x) of 0.05, 0.10 and 0.15, respectively.