Magnetic nanoparticles has many potential applications, such as ferrofluids for audio speakers, surface functionalized probes for biosensors and targeted drug delivery, magnetic storage media, powder compacts for power generation, contrasting agents in magnetic resonance imaging, and adsorbents for toxic environmental pollutants. For example, permalloy (20%iron-nickel alloy) has been the alloy of choice in magnetic devices such as thin film recording heads. Although there are many studies on electrodeposited nanoparticles, there are few systematic studies relating properties of electrodeposited iron-nickel nanoparticles. Here, we report on a study that iron-nickel nanoparticles were electrochemically synthesized from aqueous electrolytes as a function of solution chemistry, pH, and current density. Resulting nanoparticles were characterized by atomic absorption spectroscopy, X-ray diffraction, transmission electron microscopy, zeta potential, BET surface area, and magnetic property measurement. Results showed that the composition, shape, and size of Fe-Ni nanoparticles were strongly influenced by electrochemical conditions, such as solution chemistry and current density. Additionally, the composition and magnetic properties of iron-nickel alloys varied as a function of solution composition ratio of Fe3+ to Ni2+. Implications of these synthesis parameters for particle design and development will be discussed.