Thin films complex compositional alloy also referred to as thin film high entropy alloys (TF-HEAs) and are gathering increased interest for their large strength/ductility balance, owing to their single-phase FCC nanocrystalline structure [1]. Recently, CoCrNi reported hardness (H) and elastic modulus (E) up to 9 and 180 GPa respectively, due to a columnar structure with planar defects (such as staking faults) [2]. The addition of Fe – to form FexCoCrNi – led to the stabilization of the FCC phase and a small grain size of ~20 nm, affecting the mechanical behavior with a mild increase of H up to ~10 GPa [3]. However, research on TF-HEAs is still in its early stages especially concerning the film’s growth mechanisms and the relationship with mechanical behavior, while a thin film nanoengineered approach aimed to boost mechanical properties by developing new nanostructures is still an open field. In this work, we synthesized CoCrNi and Fex(CoCrNi)100-x TF-HEAs by magnetron sputtering, with controlled thicknesses from 15 nm up to 1 mm, while varying the Fe content from 15 up to 33 % at. Thick CoCrNi film shows a columnar structure with an average grain size of ~26 nm and a (111) oriented FCC structure. Additionally, we show a transition from HCP (0001) to mixed FCC/amorphous increasing thickness of 15 up to 40 nm. Nanoindentation and optoacoustic techniques report H=9.7 GPa and E=204.4 GPa in line with literature [4]. Moreover, we show that the addition of Fe retained the columnar structure while stabilizing the FCC phase reporting a preferred (111) orientation without phase segregation. Moreover, H and E decreases down to 7.5 and 176 GPa due to the lower lattice distortion as shown by a decrement in the atomic distances and higher stacking fault energy 32.5 mJ m−2 [5]. Finally, we synthesized Fe/CoCrNi (BCC/FCC) nanolaminates with bilayer period of (Λ) of 35 and 70 nm and incoherent interfaces aiming to improve mechanical properties by blocking dislocations and crack propagation. We show high adhesions at the interfaces with limited crack formation during indentation and tensile test on polymer substrate, while the H values can be finally tailored up reaching 10.5 GPa for Λ=35 nm due to the higher density of interfaces and thickness confinement. Overall, our study shed light on structure–mechanical properties of CoCrNi, Fex(CoCrNi)100-x films and Fe/CoCrNi nanolaminates with potential impacts in fields of hard coatings and microelectronics. [1] Yuanying Y, et al., J. Mater. Res. Technol, 21, 2022 [2] Yvonne (Yi-Ting) Lin, et al., Surf. Coat. Technol., Volume 424, 2021 [3] Nagy, P et al., Surf. Coat. Technol., Volume 386, 2020 [4] S.J. Tsianikas, et al., J Mater Sci Technol, Volume 39, 2020 [5] Y. Wang et al., Acta Mater, 154, 2018