Ternary alloy CdS0.65Se0.35 nanoribbons were successfully grown by a one-step thermal evaporation. The nanoribbons obtained have high-quality single-crystalline nature. To understand the whole picture of waveguide behavior in CdS0.65Se0.35 nanoribbons, we quantitatively studied the guided photoluminescence (PL) through individual CdS0.65Se0.35 nanoribbon by using scanning near-field optical microscopy (SNOM) at room temperature. The results show significant sustained red shift of PL spectra of the CdS0.65Se0.35 nanoribbons optical waveguide with the increase of the light propagation distance. According to our analysis, the red shift is attributed to the absorption of band-tail of states in nanoribbons. This finding may be extended to other ternary nanosyotems and be useful for fabricating new subwavelength photonic components.