Beta-BiOfilm photoanodes with different surface structures were prepared by oxidizing bismuth films. The physical properties were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible absorbance spectra and atomic force microscopy (AFM). XRD shows that all films are beta phase crystal structure except the thinnest 1202nm film. SEM and AFM characterizations indicate that a nanoporous surface structure is generated on the surface after the film is annealed for 302h, while the films annealed for 102h show a dense surface. The direct band gaps vary from 2.63 to 2.8802eV, with the film thickness decreasing from 500 to 1202nm. The nanoporous surface structure film exhibits better light harvesting ability and incident photon-to-electron conversion efficiency (IPCE) than the dense surface films. The IPCE (61% at 35002nm and 43% at 40002nm, 0.19702V) is the highest ever reported. The photocurrent density reaches 0.4502mA02cmwhen illuminated with a bias of 1.2302Vin 0.5M NaSO.