Nanocrystalline nickel dispersed with nano size WO 3 particles has been successfully synthesized using electrodeposition. In this synthesis, ionized WO 2-4 molecules in an electrolyte are hydrolyzed WO 3 particles and embedded into a nanocrystalline nickel matrix during electrodeposition by controlling the pH and potential of the electrode. The effect of the nano size WO 3 dispersions on the mechanical property and thermal stability of the nanocrystalline nickel is investigated in detail. The nanocrystalline nickel electrodeposited with nano WO 3 particles have the same size as the nickel matrix of approximately 25 nm and the dispersed WO 3 particles which is approximately 15 nm. The nickel electrodeposited with the WO 3 particles has a higher hardness than that without the WO 3 particles in the range of the nickel matrix grain size which is less than about 130 nm. The increase in the hardness is attributed to dispersion strengthening of nano WO 3 particles. The nickel electrodeposits with the WO 3 particles possess an increased thermal stability compared to the material without the WO 3 particles. The nickel matrix grain size of electrodeposits associated with the WO 3 particles hardly changed even after annealing for 18 ks at 573 K. The thermal stability of the nickel electrodeposits with the WO 3 particles is attributed to the Zener drag effect of nano the WO 3 particle.