Fe50Pt50 thick-films were electroplated on a Ta substrate using a direct current, and we evaluated the effect of Na ion concentration in plating baths on the magnetic properties of the annealed films. With increasing NaCl content from 2 to 30 g/L, the coercivity of the annealed Fe50Pt50 films increased from 700 kA/m to approximately 900 kA/m. For obtaining further experimental evidence for the increase in the coercivity, we employed trisodium citrate instead of NaCl as an additive in the plating bath. Consequently, as the addition of the trisodium citrate as well as NaCl increased the coercivity, we concluded that a plating bath with high Na ion concentration is effective to obtain the Fe-Pt thick-films with high coercivity.