[en] Pulsed-field gel electrophoresis has been applied to analyse the induction and repair of DNA double-strand breaks (DSB) in human hepatoma SMMC-7721 cells exposed to 3.17 MeV/u ¹⁶O⁶⁺. It shows that the DSB yields are 0.43 DSBs/100 Mbp/Gy and compared with ⁶⁰Co γ-rays, the relative biological effectiveness (RBE) of ¹⁶O⁶⁺ is 1.69. The half time of DSB fragments being repaired (t_1/2) is relevant to the dose; the higher the dose is, the longer the time is . The main way for DSB repair is the rejoining of smaller fragments into larger ones