Herein, we report the synthesis and photocatalytic properties of novel Bi2O3 nanomaterials. Cubic mesoporous films were produced by coassembly of hydrated bismuth nitrate with a poly(ethylene-co-butylene)-block-poly(ethylene oxide) diblock copolymer, referred to as KLE, while nanofiber mats were produced via electrospinning. We establish that all materials employed in this work are highly crystalline after thermal treatment and that the nanoscale order of the self-assembled samples is further retained. KLE-templated films can readily produce phase-pure beta-Bi2O3 with an optical band gap of about 3.4 eV. Calcination of nanofibers, by contrast, leads to the Formation of a composite consisting of beta-Bi2O3 and trace amounts of the thermodynamically stable alpha-Bi2O3 phase. We further show the benefits of a mesoporous morphology in heterogeneous semiconductor photocatalysis. KLE-templated beta-Bi2O3 films exhibit much greater photocatalytic activity than nanofiber mats and nontemplated Bi2O3 films (prepared under otherwise identical conditions) as well as than KLE-templated anatase TiO2 films on a mass normalized basis. We associate this exceptional activity with (I) the comparatively high BET surface area, which provides for a large number of adsorption sites, and (2) the high phase purity of the more catalytically active beta-Bi2O3.