Aim:Glioblastoma (GBM) is one of the lethal central nervous system tumors. One of the widely used chemical agents for treatment of glioblastoma is temozolomide. It is an orally administered, DNA alkylating agent. DNA alkylation triggers the death of tumor cells. However, some tumor cells are able to repair this type of DNA damage, thus lower the therapeutic effect of temozolomide. Laboratory and clinical studies indicate that temozolomide\'s anticancer effects might be strengthened when combined with other chemotherapeutic agents, like etoposide, or antioxidant agents, like ascorbic acid. In this study we aimed to evaluate the cytotoxic and oxidative stress effects of ascorbic acid (1000 µM), temozolomide (100 µM) and etoposide (25 µM) agents alone, in dual and triple combinations in the glioblastoma U87 MG cell culture.Material and Methods:The cytotoxic and oxidative stress effects were investigated by the MTT and LC MS/MS analysis methods. Results:Cytotoxicity test results showed that etoposide, temozolomide, \"etoposide + ascorbic acid\", \"temozolomide + ascorbic acid\", \"temozolomide + etoposide\" and \"temozolomide + etoposide + ascorbic acid\" combinations have antiproliferative effects. The maximum antiproliferation response was observed in the \"temozolomide + etoposide + ascorbic acid\" added group. Similarly LC MS/MS analyses showed that minimum oxidative DNA damage was occured in the \"temozolomide + etoposide + ascorbic acid\" added group.Conclusion:The results indicate that ascorbic acid decreases the cytotoxic and genotoxic effect of etoposide and etoposide-temozolomide combination, but it has no meaningful impact on the temozolomide\'s toxicity.