Tensile shear, microstructural properties of resistance spot-welded dual-phase steels having different martensite volume fractions (MVF) of 14, 17, 19 and 25% are investigated. These steels are produced from low-carbon Mn-Ni steel by air and water quenching after intercritical annealing. Joining of these steels by the resistance-spot welding method is carried out at three different welding times (10, 15, 20 cycles) while welding pressure and peak welding current are kept constant. Microstructures of the welded samples are evaluated. The tensile-shear load bearing capacity of joined samples is also determined. The experimental results show that increasing MVF increases the tensile-shear load bearing capacity at constant welding time. The weld nugget diameter is found to be extended with increasing welding cycle so the tensile-shear capacity is increased.