Cisplatin is widely used for the treatment of numerous types of cancer, while its application is limited by the adverse side effects for its poor selectivity. Trastuzumab is a highly targeting protein to HER2 protein, and it is usually combined with paclitaxel or cisplatin for the treatment of HER2-overexpressing breast cancer. In the present work, we used trastuzumab as a targeting carrier for platinum drug delivery. In ELISA assays and immunofluorescence study, Tmab-1 exhibited high and specific binding affinity to HER2 protein and HER2-overexpressing SK-BR-3 cells. In cytotoxicity test, Tmab-1 showed promising antiproliferative activity to SK-BR-3 cells, while it hardly inhibited the growth of MCF-7 cells and MDA-MB-231 cells. The cell cycle arrest study showed Tmab-1 induced the cell cycle arrest mainly at G2/M phase. This work indicates that trastuzumab is an effective and potential targeting carrier for drug delivery.