We demonstrate that Mo6S9-xIx nanowires (MoSI NWs) enable the detection of proteins with cytochrome c as a model protein using UV-vis spectrometry. The association of cytochrome c with the nanowires was verified by scanning electroctron microscopy, X-ray photoelectron, light scattering and micro-FTIR spectroscopies. Our results show that MoSI NWs is a promising nanostructure material for the development of ultrasensitive sensors for detecting proteins. The new MoSI NW derived amplification bioassay is expected to provide a straightforward and effective strategy for protein analysis and biosensor construction.