This　study　presents　the　application　of　NiO　nanoparticles　in　electrochromic　materials　field.　The　monodisperse　NiO　nanoparticles　ranged　from　5　to　8　nm　were　synthesized　by　hot-injection　method　and　the　NiO　films　were　prepared　by　dip-coating　technique　on　ITO　glass.　The　structure,　electrochemical　as　well　as　optical　performance　was　investigated　systematically.　NiO　films　composing　of　nanoparticles　maintained　the　porous　microstructure　and　exhibited　excellent　electrochromic　performance.　It　was　clear　that　the　film　annealed　at　300　degrees　C　exhibited　the　highest　electrochemical　activity　and　improved　transmittance　modulation　(Delta　T),　while　maintaining　faster　response　time.