Tungsten trioxide (WO3) has excellent mechanical properties, making them to be applied in various applications. However, researches on the mechanical properties of WO3 in the micrometer scale are limited. Here, the purpose of this study was to demonstrate nanoindentation technique in an attempt to study the micro-mechanical characteristics of monoclinic WO3 microparticles that were previously synthesized using a direct heat treatment of ammonium tungstate pentahydrate powder at a temperature of 800°C. The experiment comprises a measurement by load controlled nanoindentation test on the particle sample to obtain force and displacement relationship. The results exhibited variability on the forcedisplacement curves for similar applied load. This could be due to the micro-mechanical effects generated by the existence of inclusions, precipitates, and oxides inside the micron WO3 particles. The present study demonstrates the importance of understanding the micromechanical characteristics of WO3 for clarifying the inhomogeneity effects on its macromechanical properties.