A novel p-n junction photocatalyst of Bi4Ti3O12 nanofibers-BiOI nanosheets has been fabricated through a simple and economical technique of electrospinning combined with a successive ionic layer adsorption and reaction (SILAR) process. The products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectra (DRS), and photoluminescence (PL) spectroscopy. The as-formed Bi4Ti3O12 nanofibers are composed of inter-linked nanoparticles of 50-80 nm in size. The thickness of the as-grown BiOI nanosheets is about 10 nm and the size of the BiOI nanosheets increases with the SILAR cycles. In particular, many {001} facets of BiOI nanosheets are exposed, which is favorable to enhance the visible-light photocatalytic activity. The p-n junction photocatalyst exhibits enhanced visible-light-driven photocatalytic activity for decomposition of rhodamine B (RhB) and phenol. The enhanced photocatalytic activity can be attributed to the extended absorption in the visible light region resulting from the BiOI nanosheets and the effective separation of photogenerated carriers driven by the photo-induced potential difference generated at the Bi4Ti3O12-BiOI p-n junction interface.