The present study suggests and describes the application of a delivery system for antisense oligonucleotides against mRNA encoding estrogen receptor proteins α and β. The delivery system is composed of a cationic liposome envelope containing 17β-estradiol (E2) in its structure. Cationic liposomes protect cargo against the extracellular matrix, and E2 can increase its shuttling efficiency into cells. Using MCF-7 cells derived from estrogen receptor-positive ductal carcinoma, treatment with liposomes against ERα was found to decrease MCF-7 proliferation, and importantly the application of both the antisense against ERα and β exhibited an antiproliferative effect expressed as cell viability. Using qRT-PCR, it was shown that MT1A, NF-κB1 and K-ras genes, but not TFF1, were downregulated using E2-based liposomes (evaluated at P=0.05). Further indicators of oxidative stress were employed to assess the effect on treatment efficiency. Glutathione (GSH/GSSG redox ratio), metallothionein (MT) and malondialdehyde (MDA) confirmed a positive effect of antisense therapy resulting in their decreased levels in the MCF-7 cells. Based on these data, we suggest that E2-based liposomes offer sufficient transfer efficiency and moreover, due to the effect on NF-κB1, MT and GSH, tumor cells can be chemosensitized to increase treatment effectiveness.