Composition evolution and structural properties of Fe-Co-Ni thin films have been studied by transmission electron microscopy along the growth direction. The samples were electrodeposited with constant current from stagnant solution. The samples were of uneven composition, exhibiting two major modes of composition change: a near-substrate composition variation due to the initial transient and a non-periodic composition fluctuation attributed to the side reaction (hydrogen evolution) and the hydrodynamic instability of the stagnant solution. The microstructure of all samples showed a transition from an ultrafine-grained (on the substrate side) to a columnar growth (bulk), while a face-centered cubic - body-centered cubic two-phase structure could be seen across the entire sample thickness. The composition variation and the structural transients in the sample proved to be completely uncorrelated. (C) 2018 The Electrochemical Society.