Fast ionic conductor acting as catalyst offers an efficient choice to produce one-dimensional nanomaterial with high crystallinity and flexible tolerance for lattice mismatch. We report the colloidal synthesis of CuGaSxSe2−x nanoribbons with the assistance of Cu1.75(SSe) nanocrystals for their intrinsic nature of fast ionic conductors. The structure of the as-prepared CuGaSxSe2−x nanoribbons is hexagonal wurtzite with (001) lattice planes exposed. The composition of nanoribbons can be tuned within the broad range by changing the relative concentration of Se/OA in stock solution. By monitoring the structures, compositions, and morphologies of the nanoribbons, it is confirmed that Cu1.75(SSe) nanocrystals are formed firstly, originating from the thermal decomposition of copper diethyldithiocarbamate precursors in the presence of dodecanethiol and selenium–oleylamine, and then act as the catalysts for the growth of the nanoribbons.