Antimicrobial peptides have been widely recognized as potential candidates for treating tumor, especially for defending against multidrug-resistant cells. Previously, based on the structure of substance P, we have designed a novel class of hybrid antimicrobial peptide NS, which possesses potent antimicrobial activity against a broad spectrum of bacterial pathogens. In this study, we evaluated its cytotoxicity to tumor cells and studied the possible mechanism of action. We showed that NS could efficiently kill tumor cells by rapidly disrupting the tumor cell membrane and inhibiting the DNA synthesis. In addition, we also found that NS could efficiently deliver plasmids into cells and exhibit high transfection efficiency after the introduction of a stearyl moiety to its N-terminus, like many reported cell-penetrating peptides. Taken together, this study revealed the potential multiple functions of NS, providing fundamental support for further therapeutic application as potential antitumor agent. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.