Interfaces have been found to play an important role in mechanical behaviors of metals and alloys with heterogeneous microstructures. In present study, low C steel/304 stainless steel (SS) laminates with varying fractions of interfacial zone were fabricated by hot-rolled bonding, annealing and pickling, then cold rolling, subsequent annealing followed immediately by water quenching to study the effect of fraction of interfacial zone on the tensile properties. Heterogeneous distributions in chemical composition, grain size, phase and hardness were observed in the interfacial zone. The yield strength was observed to be constant with varying fractions of interfacial zone, while the ultimate strength and the uniform elongation were found to increase with increasing fraction of interfacial zone. High density of geometrically necessary dislocations (GNDs) were found to distribute in the interfacial zone and show a peak at the interface due to the mechanical incompatibility across the interface. Moreover, the density of GNDs was found to increase with increasing tensile strain in the interfacial zone. Back stress hardening was found to play an important role in the laminates, especially at the elasto-plastic transition stage. Higher fraction of interfacial zone can induce stronger back stress hardening and higher density of GNDs in the samples, thus resulting in better tensile ductility.