Purpose: Aim of the present study was to clarify the dependency of p53 status on migration/invasion potential of cancer cells irradiated with carbon ions. Materials and Methods: Human small cell lung cancer H1299 cells (neo: null of p53, mtp53: transfected with p53 mutant plasmid, wtp53: transfected with p53 wild type plasmid) and carcinoma A549 cells were used for experiments. Cells grown on T25 flasks in DMEM supplemented with 10% FBS were exposed to carbon ions (290MeV/n, 100keV/µm) at HIMAC. For migration/invasion assay at 24 hours after irradiation the cells were plated on culture insert membrane (8 micron pore size) coated with matrigel (1mg/ml). The number (Nm) of cells moved on lower side of membrane after 16 h were counted under microscope. Migration/invasion rate of cells was calculated as the ratio of Nm to total number of cells plated in the culture insert. Cell survivals were obtained from the colony formation assay immediately after irradiation. Results and Discussions: RBEs of H1299 and A549 cells irradiated with carbon-ions (100keV/µm) were 2.2~3.2. Migration/invasion rates of H1299neo, H1299wtp53 and H1299mtp53 irradiated with 0.5~4 Gy reduced as compared with that of uniradiated control: migration/invasion rate at 4Gy was about 60% of the control. After X-ray irradiation at 8 Gy the migration/invasion rate of H1299 and A549 cells reduced to 50~60% of the control. Present result suggests that carbon ion irradiation causes the reduction of migration/invasion potential of cells independently of p53 status of cells.