We report the synthesis and formation mechanism of In₂S₃ porous films composed of ultrathin curved nanoflakes by a simple and environment-friendly biomolecule-assisted hydrothermal process. We find that concentrations of the pH conditioner and the biomolecule glutathione significantly affect the morphology and structure of In₂S₃ films. The as-synthesized In₂S₃ porous films exhibit strong absorption in the ultraviolet region and the early visible region of the UV-Vis spectrum, with the absorption threshold around 501 nm. As compared with its dense film, the In₂S₃ porous film shows enhanced photocatalytic properties for the degradation of methyl orange due to its porous and curved nanostructures.