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-Fe 3 O 4 QDs) is reported for triple-modal bioimaging through fluorescence/magnetic resonance/computed tomography (FL/MR/CT). Especially, C-Fe 3 O 4 QDs are synthesized by using poly (γ-glutamic acid) as a precursor and stabilizer via a green and facile one-pot hydrothermal approach. The as-prepared C-Fe 3 O 4 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-Fe 3 O 4 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-Fe 3 O 4 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-Fe 3 O 4 QDs nanoprobes provides a convenient way for achieving an effective and versatile agent for tumorous bioimaging/or diagnostics.