In this work, optical and electrochemical properties of electrochromic NiO(x) films and their application to electrochromic glazing are studied. Quartz crystal microbalance (QCM) study reveals that OH- insertion/extraction occurs during coloration and bleach reaction of NiO(x) film in an organic electrolyte. This process is also confirmed by reflectance measurement by FTIR. Electrochromic glazing consisting of WO3/PEO-based Li+ electrolyte/NiO(x) system shows promising solar control properties. The possibility towards NIR-reflectance control using WO3 is exemplified.