Abstract: Image acquisition is the key technique in a computer vision-based system for the inspection of foreign fibers in lint cotton and the measurement of their contents. To construct an efficient image acquisition system for the detection and classification of those foreign fibers, spectroscopic analysis of cotton fiber and foreign fibers was performed. To detect the foreign fibers effectively, a method for selecting optimal detection bands was proposed based on the extrema distribution of reflectance differences between cotton fiber and foreign fibers. An optimal distinguishing band selection method was presented in terms of the spectrum distinguishable degree. The results indicate that the ultraviolet band is the optimal band to detect the fluorescent foreign fibers, the visible light band is the optimal one to detect color foreign fibers, and the infrared band is fit for inspecting those foreign fibers such as polypropylene and polyethylene materials, candy wrappers, hairs and feathers. The infrared band of 780-1 800 nm is optimal for distinguishing these foreign fibers.