Semiconductor synthesis and applications are of increasing interest worldwide. A simple non‐autoclave method was developed to synthesize bismuth oxyiodide (BiOI) nanoparticles and nanocomposites of BiOI/carbon nanofibers (CNFs) in propylene glycol as a solvent. The as‐prepared BiOI and its CNFs‐composites were characterized by powder X‐ray diffraction (XRD), scanning electron microscopy‐energy X‐ray‐dispersive spectroscopy (SEM‐EDX), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT‐IR), Nitrogen adsorption‐desorption‐isotherm, and UV‐vis diffuse reflectance spectra. The XRD pattern confirmed that BiOI nanomaterial was prepared successfully by the developed method. SEM and TEM analysis revealed the BiOI in its pure and composites forms possessing rose‐like nanosheets built with BiOI nanoparticles. The addition of CNFs to the BiOI in increasing mass percentage enhanced the optical properties of the BiOI‐semiconductor. The obtained results confirmed that the short‐time refluxing method prepared BiOI and BiOI/CNFs composites successfully, with the advantage of eliminating the time and energy‐consuming step of autoclave digestion. Nevertheless, the nanomaterial‘s anticancer activity was revealed when tested against breast and liver cancer cell lines and measured at 540 nm.