Sound velocities in shock-loaded solids are not only important to determine bulk moduli of solids at high pressures, but are also crucial to inform the shock melting of solids upon loading. In this letter, we first report on shock melting of porous solids at high pressures by measuring sound velocities in the porous iron of average density 6.90 g/cm3 in the pressure range of 110-180 GPa. The measured sound velocity softens at pressures from 122 to 156 Gpa, which may be attributed to shock melting of the porous iron.