Nonhazardous and value-added utilization of biomass tar remains a great challenge in biomass gasification development. Herein, both model compounds and real biomass tar were for the first time tested as the carbon source for carbon quantum dots, where the resultants demonstrated excellent monodispersibility and strong fluorescence, quantum efficiency up to 53% and 43% were achieved. Moreover, the real tar-derived CQDs further revealed as a highly selective and sensitive probe for Fe3+, indicating its great potential ion sensing. It is expected that this work would open up a new strategy for biomass tar valorization.