Multimodal imaging, which combines complementary information of two or more imaging modalities, offers huge advantages. In this paper, the synthesis, characterization, and application of superparamagnetic nitrogen-doped carbon-iron oxide hybrid quantum dots (C-Fe3O4 QDs) is reported for triple-modal bioimaging through fluorescence/magnetic resonance/computed tomography (FL/MR/CT). Especially, C-Fe3O4 QDs are synthesized by using poly (gamma-glutamic acid) as a precursor and stabilizer via a green and facile one-pot hydrothermal approach. The as-prepared C-Fe3O4 QDs exhibit excellent water dispersibility, wavelength-tunable FL property with high quantum yield of about 21.6%, good photostability, strong superparamagnetic property as well as favorable biocompatibility. Meanwhile, these C-Fe3O4 QDs also show a transverse relaxivity value (r(2)) of 154.10 mM(-1) s(-1) for T-2-weighted MR imaging mode and an observable X-ray attenuation effect for CT imaging mode. Moreover, the in vivo bioimaging of tumor-bearing nude mice by combining FL, MR, and CT images further demonstrates that the as-prepared C-Fe3O4 QDs can be readily and efficiently used in FL/MR/CT triple-modal tumor imaging. Hence, the new and facile one-pot synthesis strategy for preparing multifunctional C-Fe3O4 QDs nanoprobes provides a convenient way for achieving an effective and versatile agent for tumorous bioimaging/or diagnostics.