The microstructure and mechanical properties studies of a series of two-phase f.c.c./B2 lamellar-structured, high-entropy FeNiMnAlTi alloys with up to 6 at. % Ti has been studied. X-ray microanalysis in a TEM showed that the Ti resided mostly in the B2 phase. The lamellar spacing decreased significantly with increasing Ti content, leading to a sharp increase in room-temperature strength, - the yield strength exhibiting a Hall-Petch-type relationship with the lamellar spacing - but with a concomitant decrease in ductility. Annealing the alloy at 823 K for 24 h increased the yield stress to ~1000 MPa, while the yield stress was greatly reduced by annealing at 1173 K for 20 h due to the increase in lamellar spacing. Softening of the B2 phase at 973 K, resulted in a significant decreases in strength at that temperature irrespective of Ti content, but increases in ductility.