An integrated Bi2O3 (i-Bi2O3) nanostructure with a particle size 10 nm inducing agglomerated structure were synthesized by dissolving bismuth nitrate pentahydrate in diethylene glycol at 180 ℃ with post heat treatment. The prepared i-Bi2O3 nanostructures were employed for the construction of Au/i-Bi2O3 composite system and characterized by X-ray diffraction patt, UV–visible diffuse reflectance spectroscopy (DRS), and transmission electron microscopy, X-ray photoemission spectroscopy (XPS) and Energy dispersive X-ray spectroscopy (EDS). The i-Bi2O3 nanostructure and Au/i-Bi2O3 composite system were found to exhibit high photocatalytic activity than commercial Bi2O3 in decomposing salicylic acid under visible light irradiation. The high catalytic activity of i-Bi2O3 nanostructure was deduced to be caused by charge separation facilitated by electron hopping between the particles within the integrated structure and space-charge separation between i-Bi2O3 and Au. The charge separation behavior in i-Bi2O3 nanostructure was further bolstered by comparing the measured. OH radical produced in the solution with i-Bi2O3 nanostructure, commercial Bi2O3 and Au/i-Bi2O3 composite which readily react with 1,4-terephthalic acid (TA) inducing 2-hydroxy terephthalic acid (TAOH) that shows unique fluorescence peak at 426 nm. The space-charge separation between i-Bi2O3 and Au was confirmed by measuring the electron spin resonance (ESR) spectra.