Electrochemical, spectroscopic, and structural measurements were used to characterize the electrochromic behavior and stability of electrodeposited MoO3 thin films. These films are prepared from metal/hydrogen peroxide solution on transparent conductive glass (i.e., ITO). The as-deposited films are partially crystalline and show an improvement in crystallinity after heat-treatment in air at 260 degrees C. These films display reversible electrochromic properties from blue to clear, when cycled in a 1 M solution of lithium perchlorate in propylene carbonate between -0.5 and +2.5 V. The observed effects of heat-treatment on the electrochromic properties are discussed and related to x-ray photoelectron spectroscopy analysis. The elemental depth profiles of colored MoO3 films were analyzed by secondary ion mass spectrometry.