Halobenzoquinones (HBQs) are an emerging class of halogenated disinfection byproducts (DBPs) in drinking water, which raised public concerns due to potential carcinogenic effects to human bladder. Our previous work demonstrated that HBQs and hydrogen peroxide (H2O2) together generated oxidative DNA damage via a metal-independent and intercalation-enhanced oxidation mechanism in vitro. This study further investigated the efficiency of various HBQs to induce oxidative DNA damage in T24 bladder cancer cells. Compared with T24 cells without treatment (3.1 lesions per 106 dG), the level of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG) significantly increased by 1.4, 3.2, 8.8, and 9.2 times after treatment with tetrabromo-1,4-benzoquinone (TBBQ), terachloro-1,4-benzoquinone (TCBQ), 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) and 2,5-dichloro-1,4-benzoquinone (2,5-DCBQ) for 24 hr, respectively. Interestingly, we found that the oxidative potency of HBQs in T24 cells (2,5-DCBQ ≈ 2,6-DCBQ > TCBQ > TBBQ) is inconsistent with that of in vitro dsDNA oxidation (TCBQ > TBBQ > 2,5-DCBQ > 2,6-DCBQ), suggesting HBQs induce oxidative lesions in cellular genomic DNA probably involved with a complex mechanism.