Glioblastoma (GBL) is one of the more malignant primary brain tumors, currently treated by a multimodality strategy including surgery, radio- and chemotherapy, mainly consisting of Temozolomide(TMZ)-based chemotherapy. Tumor relapse often occurs due to the establishment of TMZ resistance, with a patient median survival <2 years. The identification of natural molecules having strong anti-tumor activity, led to combine these compounds with conventional chemotherapeutic agents, developing protocols of integrated anticancer therapies. Curcumin (CUR), Resveratrol (RES), and its glucoside Polydatin (PLD) are widely employed in the pharmaceutical and nutraceutical fields, and several studies demonstrated that the combination of these natural products was more cytotoxic than the single compound alone in different cancers. Some of us recently demonstrated the synergistic efficacy of the sublingual administration of a new nutraceutical formulation of CUR+PLD in reducing tumor size and improving GBL patient survival. To deepen some mechanistic aspects of these results, we investigated if the pretreatment with a combination of CUR+PLD, can improve TMZ cytotoxicity on GBL cells, by analyzing the effects on cell cycle, viability and morphology, on proteins related to cell proliferation, differentiation, apoptosis or autophagy, and on actin network. Cell viability was assessed by MTT or by the cell counter CytoSmart. CalcuSyn software was used to study the CUR+PLD synergism. Morphology was evaluated by optical and scanning electron microscopy, and protein expression was analyzed by Western Blot. Flow cytometry was used for cell cycle, autophagic flux, and apoptosis analyses. The results obtained provide evidence that CUR and PLD, acting in synergy with each other, strongly improve the efficacy of alkylating antitumor agents such as TMZ, also in drug-resistant GBL cells, through their abilities to affect survival, differentiation, and tumor invasiveness.