Tungsten oxide thin films were prepared by solution thermolysis (ST-WO,). Films were deposited onto fluorine-doped tin oxide (FTO)-coated glass substrates maintained at 300 degreesC, which were then used as working electrodes in a three-electrode electrochromic (EC) cell. The EC cell configuration was FTO/WO3/0.1 N H2SO4/C, SCE. Cyclic voltammetry (C-V) was carried out in the potential range -0.7 to +0.7 V (SCE), at different scan rates. The values of anodic peak potential and threshold voltage are extracted from C-V. The diffusion coefficient of H+ ions during intercalation and deintercalation are calculated. They are of the order of 10(-12) cm(2)/s. Chronoamperometric (C-A) studies were carried out at different double potential steps and response times are calculated. The films before and after colouration were further characterized by optical absorption technique. The colouration efficiency at 633 nm is 25 cm(2)/C. The ST-WO3 films were found to be stable in 0.1 N H2SO4 up to 2X10(3) cycles.