In this study, we present a synthetic method for the preparation of oxo-graphene nanoribbons (oxo-GNRs) by oxidative cleavage of C–C bonds of enriched (6,5)-single-walled carbon nanotubes (SWCNTs). We applied a mild oxidation protocol to oxidize SWCNTs involving sulfuric acid as dispersion medium and potassium permanganate as oxidant. The obtained oxo-GNRs exhibit stunning fluorescence properties with emission maxima of about 300 nm and 400 nm, respectively, depending on oxidation time. The analyses reveal that functional oxo-groups are predominantly located at the rims of oxo-GNRs. Next to lactones, 1,3-ketones are identified, which can be further reacted with hydrazine, most likely forming pyrazoline groups. Based on our data, we propose a chemical structure model for the oxo-GNRs. The model is based on an intact inner π-system, responsible for photoluminescence properties and oxo-functionalized rims of GNRs.