High-quality ultra-long alloyed CdSxSe1-x (0 <= x <= 1) whiskers were obtained by a simple thermal evaporation route. The near band-edge emission in these whiskers can be effectively guided at the sub-millimeter scale under continuous-wave laser excitation. As good optical waveguide cavities, the whiskers exhibit stimulated emissions under pulsed light excitation at room temperature for all compositions 0 <= x <= 1. The spectral positions of the sharp emission lines of the whiskers were tuned by their compositions, covering the spectral range from green to red.