The Rev peptide that binds to nucleophosmin/B23 with the highest affinity exhibits the greatest cytotoxicity on Ras-3T3 cells and inhibits tumor growth most effectively in nude mice. The efficiency of colony formation in soft agar of Ras-3T3 cells is significantly inhibited by treatment with Rev peptide. In addition, Rev peptide can potentiate the doxorubicin-induced decrease of cellular viability in U1 bladder cancer cells and inhibition of tumor growth in nude mice. Treatment of Rev peptide increases protein expression and transcriptional activity of p53 and inhibits the nucleophosmin/B23-mediated PCNA promoter activation. Peptides having high affinity of binding to molecular targets such as nucleophosmin/B23 represent a useful approach to anti-cancer biotherapeutics.