The study was aimed at evaluating antitumor and immunomodulatory effects of liposomal vaccine composed of P5 human epidermal growth factor receptor 2 (HER2)/neu‐derived peptide coupled to the surface of high‐temperature nanoliposomes containing distearoylphosphocholine:distearoylphosphoglycerol:Chol:dioleoylphosphatidylethanolamine (DOPE) comprising monophosphoryl lipid A (MPL) adjuvant in HER2/neu overexpressing the breast cancer model. BALB/c mice bearing TUBO carcinoma were subcutaneously immunized with formulations containing 10 µg P5 peptide and 25 µg MPL three times with 2‐week intervals. To determine immuno responses in immunized mice, the amount of released interferon‐γ and IL‐4 were measured by the enzyme‐linked immunospot method and the flow cytometric analysis on the isolated splenocytes. The results demonstrated that tumor‐bearing mice immunized with Lip/DOPE/MPL/P5 formulation had the most released interferon‐γ and the highest cytotoxic T lymphocyte responses that led to the lowest tumor size and the longest survival time than those of other formulations. The results achieved by Lip/DOPE/MPL/P5 formulation could make it a suitable candidate to induce effective antigen‐specific tumor immunity against breast cancer.