The efficacy of two carbon-based nanomaterials, graphene oxide (GO) and Ti3C2 MXene (MX), on the radiosensitivity of the breast cancer cells (BCC) was investigated using clinical X-ray irradiation. The prepared GO and MX nanoparticles (NPs) were firstly characterized utilizing FT-IR, UV-Vis, AFM and TEM techniques and subsequently assessed in terms of their radiobiological properties. The results of the cell toxicity assay indicated that neither NPs exhibited significant cytotoxicity after 48 h incubation with BCC up to 50 µg/mL concentration without irradiation. The cell internalization results showed an approximately equivalent cellular uptake for both NPs after 6 h incubation with BCC. Our comparative studies with radiotherapy demonstrated that both NPs substantially increased cell proliferation inhibition and cell apoptosis of BCC under X-ray irradiation when compared to BCC treated with irradiation alone. Additionally, the DCFH-DA flow cytometry results and fluorescent microscopy images revealed that both NPs remarkably increased the level of intracellular reactive oxygen species (ROS) generation in BCC under X-ray irradiation. The MX nanosheets exhibited superior radiosensitization efficiency than GO under X-ray irradiation due to its higher level of intracellular ROS generation (MX = 75.2 % and GO = 65.2 %). Clonogenic cell survival assay and extracted radiobiological parameters revealed that both NPs in combination with X-ray irradiation induced more lethal damage and less sublethal damage to BCC. Generally, the obtained results demonstrate that the MX NPs, as a stronger radiosensitizer than GO, could be a promising candidate for enhancing the effectiveness of radiotherapy in breast cancer treatment.