Investigation of the microstructure and mechanical properties of FeNiMnCuxAl0.1Ti0.1 (x = 0.5, 1.0, & 1.5) high entropy alloys (HEAs) with increasing Cu content has been carried out. As-cast alloys were subjected to solutionization treatment at 1000 °C for 24 h to achieve a single-phase and then cold rolled to a thickness reduction of 85%. As-cast HEAs consist of two FCC phases, i.e., Fe-rich dendritic phase & Cu-rich interdendritic FCC phase and a small number of intermetallic particles. The presence of these phases was correlated using ThermoCalc calculations, X-ray diffraction (XRD), and scanning electron microscopy (SEM) studies. Phase separation is due to the positive enthalpy of mixing of Cu and Fe elements in the alloy. After the heat treatment, the Cu-rich inter-dendritic phase dissolved and formed a single FCC phase. The yield strength and tensile strength of the cold-rolled HEAs are found to increase with the increase in Cu content. Tensile strength of the HEAs increases from 708 to 900 MPa with the increase of Cu content from 0.5 to 1.5, respectively. Strain hardening was observed in the alloys before failure due to the hindrance of dislocation motion by the presence of the massive number of dislocations accumulated during cold rolling and from the intermetallic particles.