[en] Tungsten trioxide (WO₃) has been investigated extensively because of its photochromic and electrochromic properties, which allow its color to be changed easily under various conditions. This research reports the pressure-induced chromism of WO₃ nanoparticles under pressures from ambient pressure to 31.8 GPa, in an effort to establish the pressure-structure-coloration relationship of WO₃ nanoparticles. In situ Raman spectra were used to evaluate the phase structures; and in situ UV–vis absorption spectra were utilised to characterise the coloration performance of the WO₃ nanoparticles. The phase transition and coloration characteristics of the nanoparticles were investigated in comparison with microcrystalline WO₃, based on the Raman results, and a series of phase transition sequences, associated with irreversible color change, was observed under different pressures. (paper)