The synthesis of nanoscaled β-Bi2O3 starting from the bismuth oxido clusters [Bi6O4(OH)4](NO3)6·H2O, [Bi22O26(OSiMe2tBu)14], [Bi38O45(NO3)20(DMSO)28](NO3)4·4DMSO and [Bi38O45(OMc)24(DMSO)9]·2DMSO·7H2O (OMc = O2CC3H5) under ambient conditions is reported. The metal oxido clusters are regarded as ideal precursors for β-Bi2O3 due to their structural relationship with the latter. Nevertheless, different bismuth oxide polymorphs are accessible dependent on the hydrolysis protocol. Hydrolysis over a period of 18 h gave stable α-Bi2O3 whereas after 3 min an amorphous material is observed. Annealing of the amorphous material at 370 °C gave nanoscaled β-Bi2O3. An unusual high reactivity of the β-Bi2O3 particles with SiO2 and Al2O3 is observed at temperatures above 400 °C. Powder X-ray diffraction studies, transmission electron microscopy, diffuse reflectance UV/Vis spectroscopy and nitrogen adsorption measurements are used for characterization of the as-prepared β-Bi2O3 nanoparticles. The properties of the β-Bi2O3 nanoparticles depend on the starting bismuth oxido clusters with regard to particle size and optical band gap. The β-Bi2O3 nanoparticles show excellent photocatalytic activity as demonstrated by dye decomposition (rhodamine B, methyl orange, methylene blue and orange G) under visible light.