The influence of uniaxial strain on structure, magnetic, electronic, elastic, ferroelectric and piezoelectric properties of corundum double oxides Mn2MnB'O6 (B′ = Mo, Sb) is investigated using first principle calculations. These compounds have six independent sites occupied by Mn1, Mn2, Mn3, Mo/Sb, O1 and O2 ions. Ferrimagnetic (FiM) is the favorable ground state magnetic phase due to difference in magnetic moments of cation face sharing octahedra. The strain confined the magnetic orbital and led to reduced the strength of AFM coupling, which results in magnetic phase transition from FiM to ferromagnetic. These compounds are found semiconductors with band gap values 1.18 and 0.63 eV for Mn2MnMoO6 and Mn2MnSbO6 respectively. The narrowness and wideness in the band gap is observed with tensile and compressive strain respectively. The strain-free elastic constants revealed that these compounds are stable in rhombohedral crystal symmetry, linearly decrease occurred in elastic constants, with compressive to tensile strain. The calculated high values of spontaneous polarization 63.28 and 31.64 μC/cm2 make these materials suitable candidates for ferroelectric application. Polarization in these compounds is reversible with strain. The larger values of piezoelectric coefficient reveal that these compounds are good lead-free piezoelectric materials.