Polydopamine (PDA) preserves universal coating and metal-binding ability, and is suitable for application in synthesizing multifunctional agents. Herein, utilizing mesoporous silica assisted deposition to enhance both heterogeneous nucleation and loading amounts of PDA, the magnetic resonance (MR) T component (PDA-Fe) and MR T/computed tomography (CT)/multiphoton luminescence (MPL) component (FePt) have been successfully integrated in aqueous solution. This four-in-one (T, T, CT, MPL) imaging nanocomposite, FePt@mSiO @PDA-polyethylene glycol (PEG), demonstrated its multi-imaging power both in vitro/in vivo. According to our in vitro/in vivo results, FePt@mSiO@PDA-PEG reveals water-content-dependent property in T MR imaging, which suggests the necessity of having dual-modal MR ability in a single particle for the precision diagnosis. Most importantly, this dual (T,T)-MRI/CT contrast agent is demonstrated complementary to each other in the in vivo testing. PDA coated mesoporous silica also offers an advantage of delayed degradation that prevents adverse effects caused by silica fragments before excretion. The potential of this nanocomposites in both drug carrier and photothermal agent was further evaluated by using doxorubicin and monitoring solution temperature after irradiating 808 nm continuous-wave, respectively The merits of controlled polymerization, enhanced PDA loading, and biofavorable degradation make this methodology promising to other nanoparticle@mSiO for a wide range of bioapplications.