The purpose of the present study was to evaluate the toxicity of gold nanoparticles (AuNPs) incorporated into branched polymer matrices Dextran-graft-Polyacrylamide on cancer cells of different origin. The study was performed on breast cancer MCF-7 cell line and its two sublines MCF-7/Dox and MCF-7/DDP resistant to Dox and DDP, respectively and MT-4 (human T-cell leukemia) cell line. All cells were treated with copolymer D-g-Paa alone and nanosystem, containing D-g-Paa/AuNPs. Results of our study proved low toxicity of examined compounds even in high doses. Nanosystems, containing AuNP exhibited more pronounced cytotoxic effects on cancer cells in comparison to D70-Paa alone.