To develop more biomarkers for diagnosis and therapy of ovarian cancer, a 12-mer phage display library was used to isolate peptides that bound specifically to the human ovarian tumor cell line SK-OV-3. After five rounds of in vitro screening, the recovery rate of phages showed a 69-fold increase over the first round of washings and a group of phage clones capable of binding to SK-OV-3 cells were obtained. A phage clone named Z1 with high affinity and specificity to SK-OV-3 cells was identified in vitro. More importantly, the synthetic biotin-labeled peptide, ZP1 (=SVSVGMKPSPRP), which corresponded to the sequence of the inserted fragment of Z1, demonstrated a high specificity to SK-OV-3 cells especially when compared to other cell lines (A2780 and 3T3). ZP1 might therefore be a biomarker for targeting drug delivery in ovarian cancer therapy.