In this study, we successfully developed a BsAb (mPEG × HER2) which can simultaneously recognize mPEG molecules on the surface of mPEGylated nanomedicine (i.e., PLD) and the HER2 antigen on the surface of ovarian cancer cells, and easily provide HER2+ tumor specificity to PLD by a simple mixing procedure. Here, ERBB2 is linked to ovarian carcinoma.