The aim of this study was to investigate protective effects of the lipophilic vitamin C derivative, 6-o-palmitoylascorbate (PlmtVC), against X-ray radiation-induced damages including cell death, DNA double-strand breaks (DSBs), lipid peroxidation, and protein carbonylation in human lymphocytes HEV0082, and the stability of PlmtVC under cell-cultured or cell-free condition. Irradiation with X-ray (1.5 Gy) diminished the cell viability and induced apoptosis, both of which were protected by pre-irradiational administration with PlmtVC. Gamma-H2A.X foci as a hallmark of DSBs were markedly enhanced in the irradiated cells. PlmtVC prevented X-ray-induced DSBs more appreciably than L-ascorbic acid (L-AA). Intracellular ROS production, lipid peroxidation, and protein carbonylation in HEV0082 cells were increased by X-ray at 1.5 Gy, all of which were significantly repressed by PlmtVC. PlmtVC also elevated endogenous reduced glutathione (GSH) in HEV0082 cells, and prevented X-ray-induced GSH depletion that are more appreciably over L-AA. Thus, PlmtVC prevents X-ray-induced cell death through its antioxidative activity. Stability tests showed that after being kept under physiological conditions (pH 7.4, 37 °C) for 14 days, vitamin C residual rates in PlmtVC solutions (62.2-82.0 %) were significantly higher than those in L-AA solutions (20.5-28.7 %). When PlmtVC or L-AA was added to HEV0082 lymphocytes, intracellular vitamin C in L-AA-treated cells was not detectable after 24 h, whereas PlmtVC-treated cells could keep a high level of intracellular vitamin C, suggesting an excellent stability of PlmtVC. Thus, X-ray-induced diverse harmful effects could be prevented by PlmtVC, which was suggested to ensue intrinsically from the persistent enrichment of intracellular vitamin C, resulting in relief to X-ray-caused oxidative stress.