The plasmonic and magneto-plasmonic nanocomposites are multi-functional structures that are applicable to medical applications such as tumor therapy, diagnosis, and biosensors. Here, the simulation of the optical and photothermal properties of plasmonic nanocomposites has been done. The spherical core@shell and core/shell@shell nanocomposites have been modeled using the generalized Mie theory. Au and Fe2O3 have been used as plasmonic and magnetic structures because of their bio-compatibility and then the role of MoS2 shell has been examined. The results show that these structures are very effective in photothermal therapy since their localized surfaced plasmon resonance is situated in the near-infrared region of electromagnetic waves. Among the simulated structures, Fe2O3@Au shows the best plasmonic behavior and absorption efficiency enhanced about 7 when the core radius is 20 nm, and the shell thickness and wavelength of incident light are between 5 and 10 nm and 700–800 nm, respectively. Maxwell-Garnett's effective medium theory has been used to calculate the effective permittivity of nanocomposites as well as the simulation of the temperature increase under laser radiation. The temperature enhancement of single nanocomposites shows very promising results. The single Fe2O3/Au@MoS2core/shell@shell nanocomposite illustrates the highest performance in temperature increase with 10−3K.