Breast cancer is one of the most serious diseases, posing threats to women's physical and mental health. Gene therapy has been gradually regarded as an important part of tumor therapeutics. In the present study, the breast cancer‑specific gene 1‑small interference RNA (BCSG1‑siRNA) plasmid was designed, then encapsulated by chitosan‑silicon dioxide nanometer carriers. The results demonstrated a successful encapsulation of BCSG1‑siRNA in chitosan‑silicon dioxide nanoparticles (encapsulation efficiency exceeded 90%). BCSG1‑siRNA was released slowly (the release rate was almost 30% after 24 h). The cytotoxic effect on MCF‑7 cells was enhanced by increasing the concentration of nanoparticle (the proliferation rate was reduced to 13.4±5.3% and apoptosis rate was increased to 71.5±6.8%). Therefore, the materials presented in the current study acted as successful gene carriers and exhibited significant antitumor effects in breast cancer cells.