Propous thin films of Bi2O3/Bi2S3 nanocomposite semiconductors were prepared rapidly at gas/liquid interface for the first time by contacting an acidic Bi(NO3)(3) solution with vapors from ammonia water and ammonium sulfide solution. Hydrolysis of Bi3+ into Bi2O3 nanoparticles (NPs) and their partial sulfurization into Bi2S3 occurred at/near the solution surface upon contacting the vapors of NH3 and H2S, respectively. Based on photoelectrochemical performances, the conditions were optimized for preparation of Bi2O3/Bi2S3 thin films by interfacial reactions and self-assembly of the in situ produced nanocomposites, including concentrations of Bi(NO3)(3) and HNO3, vapor sources, contact manners and contact times. The porous thin film of Bi2O3/Bi2S3 prepared under optimized conditions showed better photoelectrochemical performance than the respective thin films of Bi2O3 and Bi2S3 and their some other composites. (C) 2014 Elsevier B.V. All rights reserved.