Stress generation was examined during the electrodeposition of NixPt1-x alloys from 0.5 M NaCl + 3 mMK(2)PtCl(4) + 0.1 M NiCl2 (pH = 2.5), using the wafer curvature method, in films measuring less than 50 nm in thickness. Steady state tensile stress, ranging from 0.5 to 1.4 GPa, developed in the NixPt1-x films and showed a strong dependence on electrode potential. Deposit grain size, measured by XRD line broadening, appears to be independent of deposition potential, suggesting that nuclei coalescence, though a primary source of tensile stress, does not determine its dependence on the potential. However the steady state stress of the Ni-rich alloys shows a strong growth rate dependence, similar to that of pure Ni, which is consistent with an increase in free volume that can be associated with grain boundaries, as well as vacancy or vacancy cluster formation. Steady state stresses as large as 1.4 GPa can be generated in 35 nm Ni-rich electrodeposits. However, these large stresses can be reduced by 35% if the composition of the film is changed incrementally. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.073208jes]