We explore a novel method to synthesize pebble-like nanocrystalline WO3 thin films for the first time by thermal decomposition of a multilayer Langmuir –Blodgett film of an octadecylamine –tungsten complex. The resulting film was thoroughly characterized by various characterization techniques. The electrochromic performance was evaluated in Li + as a charge-balancing ion. The WO3 thin film displays a state-of-the-art performance with respect to optical modulation of 25.94% at λ630 nm with a very rapid coloration and bleaching time of 3.57 s and 3.14 s, respectively and a high coloration efficiency of 71.26 cm2C-1. The excellent electrochromic performance can be attributed to the high size uniformity of WO3 nanoparticles, whose crystalline nature offer more active sites for Li+ diffusion and control the diffusion path length. Thus, the Langmuir–Blodgett WO3 film contributes to high energy conversion devices.