The present research work has concentrated to synthesize nanocrystalline (NC) Cr0.26Fe0.24Al0.5 (medium entropy alloy, 3E-MEA) and Cr0.15Fe0.14Al0.30Cu0.13Si0.28 (high-entropy alloy, 5E-HEA) non-equiatomic (equal weight fraction) alloys through mechanical alloying (MA); which studied the influence of entropy effect on structural properties, microstructural characterization, and mechanical behaviour. Further, the same non-equiatomic ratio of two coarse grain alloys (CGAs) was manufactured by conventional powder metallurgy (PM) route (blending method, 3E-CGA, 5E-CGA) for comparison. All synthesized powders were hot-pressed (HPed) at 723 k for 30 min subsequently mechanical properties in terms of compres- sive stress-strain and hardness were examined. The samples of as-milled powders, HPed, and fractured were investigated using X-ray diffraction (XRD) and advanced electron microscopes. The HPed sample of 3E-MEA of Cr0.26Fe0.24Al0.5 produced 94% BCC and 6% FCC crystal structures due to more dissolution of Al atoms in the stronger bonding atoms of Cr-Fe lattice. Whereas 5E-HEA of Cr0.15Fe0.14Al0.30Cu0.13Si0.28 sample has exhibited 72.1% FCC phase and 27.9% BCC phase due to balance between the dissolution of FCC elements (Al, Cu, Si) and BCC elements (Cr, Fe). Further, 3E-MEA and 5E-HEA have exhibited the ultimate compressive strength (UCS) of 1278 ? 6.75 MPa and 2060 +/- 2.8 MPa respectively whereas the corresponding conventionally blended alloys produced 268 +/- 5 MPa and 615 +/- 3 MPa for 3E-CGA and 6E-CGA respectively. Vicker?s hardness strength (VHS) of 5E-HEA of Cr0.15Fe0.14Al0.30Cu0.13Si0.28 has exhibited 68% more when compared to 3E-MEA of Cr0.26Fe0.24Al0.5, 3.26 times higher compared to blended alloys. Further, several strengthening mecha- nisms on the mechanical behaviour of MEA and HEA were investigated in which dislocation strengthen- ing mechanisms followed by solid solution strengthening mechanisms have influenced more as compared to grain boundary strengthening mechanisms. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.