Glioblastoma multiforme (GBM) is the most common and most aggressive brain tumor. Despite multimodal therapy, the prognosis for GBM patients is very poor due to the diffuse growth and therapy resistance of hypoxic areas. Betulinic acid (BA), a natural substance of plane trees, has a selective cytotoxic and radiosensitive effect and is a potential substance for tumour therapy. Due to its poor solubility, however, the therapeutic use of BA is limited. Derivatives with improved solubility and modified properties were synthesized by chemical modification. The cell and radiation biological effects of the BA and BA cisplatin derivatives DE9B and APC in GBM cell lines were investigated under normoxia and hypoxia. The analyses showed that both APC and BA have a stronger cytotoxic and radiosensitive effect in hypoxia. DE9B, the most cytotoxic substance, showed no improved effect or radiosensitization under hypoxia. Both derivatives induced apoptosis, necrosis and autophagy to varying degrees depending on the cell line and oxygen content, but not the cell cycle.