CdSe/ZnS-quantum-dot doped fibers (QDF) are prepared. By measuring the photoluminescence (PL) spectra of the QDFs with various doping concentrations and fiber lengths, the red shift of the PL peak wavelength of the QDFs is observed, which is dependent on the doping concentration and the fiber length. The red shift as a function of fiber length in four fiber-core materials (toluene, ultraviolet curable adhesive, hexane and decane) is determined. Although the increase/decrease rate of the red shift depends on the core material and the doping concentration, the maximum red shift even approaches to an identical saturation value (20 nm), which is correlated with the full-width at half-maximum(FWHM) of the first absorption peak of the QD.