a Multifunctional hybrid nanoparticles (NPs, ∼100 nm) that combine magnetic Fe 3 O 4 nanocrystals and flu-orescent carbon dots (CDs) in porous carbon (C) were successfully synthesized using a one-pot sol-vothermal method by simply increasing the H 2 O 2 concentration. The resultant Fe 3 O 4 @C-CDs hybrid NPs not only demonstrate excellent magnetic responsive properties (M s = 32.5 emu g −1) and magnetic reson-ance imaging ability (r * 2 = 674.4 mM −1 s −1) from the Fe 3 O 4 nanocrystal core, but also exhibit intriguing photoluminescent (quantum yield ∼6.8%) properties including upconversion fluorescence and excellent photostability from the CDs produced in the porous carbon. The hybrid NPs can enter the intracellular region and illuminate mouse melanoma B16F10 cells under different excitation wavelengths. Meanwhile, the mesoporous carbon shell and hydrophilic surface functional groups endow the hybrid NPs with high loading capacity (835 mg g −1) for the anti-cancer drug doxorubicin and excellent stability in aqueous solutions. More importantly, the hybrid NPs can absorb and convert near-infrared (NIR) light to heat due to the existence of CDs, and thus, can realise NIR-controlled drug release and combined photothermo/ chemotherapy for high therapeutic efficacy. Such nanostructured Fe 3 O 4 @C-CDs hybrid NPs demonstrate great promise towards advanced nanoplatforms for simultaneous imaging diagnostics and high efficacy therapy.