A combination of dual-mode imaging, such as magnetic resonance imaging (MRI) and fluorescence imaging (FI), can solve the issues about single-model imaging, such as low sensitivity and lower resolution, and provide more accurate information for clinical diagnosis. This study aims to synthesize a Zn-doped Fe3O4-LCysteine@ Nitrogen-doped Graphene Quantum Dots (N-doped GQDs) nanocomposite with high magnetic properties and suitable optical characteristics for a wide range of biomedical applications, especially as a contrast agent for MRI/FI. To synthesize hybrid magneto-fluorescent nanoparticles, Zn-doped Fe3O4 nanoparticles were first synthesized using a co-precipitation method, and their surface was functionalized with L-cysteine. Then, the composite is formed by incorporating N-doped GQDs, which are synthesized by a hydrothermal method. They possess an average size of 19 ± 3 nm with strong and excitation-independent PL emission at about 525 nm with a saturation magnetization of ~ 34 emu/gr. In vitro studies for L929 fibroblast cells reveal that nanocomposites are not toxic up to a high 100 µg/mL concentration. Therefore, the developed Zn-Fe3O4-LCys@N-GQDs offer great potential for dual-mode imaging of cancerous tumours.