Purpose: Expanded research on the biomedical applications of graphene has shown promising results, although interactions between cells and graphene are still unclear.The current study aims to dissect the cellular and molecular effects of graphene nanocomposite in photothermal therapy against cancer, and to evaluate its efficacy.Methods: In this study, a reduced graphene oxide and iron oxide (rGO-Fe 3 O 4 ) nanocomposite was obtained by chemical synthesis.The nanocomposite was fully characterized by Raman spectroscopy, TEM, VSM and thermal profiling.Cell-nanocomposite interaction was evaluated by confocal microscopy and viability assays on cancer cell line HeLa.The efficacy of the thermal therapy and changes in gene expression of Bcl-2 and Hsp70 was assessed. Results:The resulting rGO-Fe 3 O 4 nanocomposite exhibited superparamagnetic properties and the capacity to increase the surrounding temperature by 18-20°C with respect to the initial temperature.The studies of cell-nanocomposite interaction showed that rGO-Fe 3 O 4 attaches to cell membrane but there is a range of concentration at which the nanomaterial preserves cell viability.Photothermal therapy reduced cell viability to 32.6% and 23.7% with 50 and 100 µg/mL of nanomaterial, respectively.The effect of treatment on the molecular mechanism of cell death demonstrated an overexpression of anti-apoptotic proteins Hsp70 and Bcl-2 as an initial response to the therapy and depending on the aggressiveness of the treatment. Conclusion:The results of this study contribute to understanding the interactions between cell and graphene and support its application in photothermal therapy against cancer due to its promising results.