Thin film high entropy alloys (TF-HEAs) are gaining attention for their large ductility and yield strength, as a result of their small grain size and the activation of mechanical size effects [1]. Moreover, hardness and yield strength can be improved by developing nanolaminate structures, capable of blocking dislocations and crack propagation at the interfaces [2]. However, developing new nanoarchitectures and investigating local mechanical properties using in situ SEM techniques is still an open challenge. In this work, we developed nanoarchitectured TF-HEAs by magnetron sputtering and pulsed laser deposition (PLD) in combination with thermal annealing treatments, enabling a fine control over the film’s morphology while also developing nanolaminated structures with precise control of the interface density. Firstly, we focus on the synthesis of nanostructured CoCrCuFeNi TF-HEAs by PLD. We report a transition compact → nanogranular for a background pressure >1 Pa (Fig.1), resulting in a mild density decrement due to cluster-assembled growth (down to 6.91 g/cm3). Moreover, these films show greater hardness (10.5 GPa) compared to magnetron sputtering (7.4 GPa), while showing exceptional ductility in tensile tests on polymer substrate (onset of crack formation at ε=3.4%). Thermal annealing (investigated by in situ XRD) shows grain coarsening starting from 400°C and the formation of a FeCu3 phase, resulting in H decrement (down to 8.5 GPa). Secondly, we fabricated Al/HEA nanolaminates with bilayer period (Λ) ranging from 2.5 to 200 nm. Among the main results, we show that Al/CoCrCuFeNi nanolaminates (semicoherent, FCC/FCC) maintain high hardness, up to 9.7 GPa (Λ=50 nm) despite a volume fraction of 50% for Al (H≈1.5 GPa), while Al/Al25(CoCrCuFeNi)75 (incoherent, FCC/BCC) show high ductility (no brittle fractures at 30% deformation) and a yield strength of 2.5 GPa. Overall, our results show how a nano-engineer design of TF- HEAs results in improved and tunable mechanical properties with key implications for industry applications. [1] Zou, Y., et al., Ultrastrong ductile and stable high-entropy alloys at small scales. Nat. Com. 6: 2015 [2] Sàenz-Trevizo, A., et al., Nanomaterials by design: a review of nanoscale metallic multilayers Nanotechnology, 31, 2020