A novel, simple and sensitive fenitrothion (FT) sensor was developed based on as-synthesized peptide nanotubes (PNTs) on modified pencil graphite electrode (PGE). This modified electrode (PNT/PGE) was characterized by SEM, electrochemical impedance spectroscopy and cyclic voltanunetry techniques. The electrochemical response of the PNT/PGE was linearly proportional to the concentration of FT over the range of 0.114 mu M to 1.712 mu M with a lower detection limit of 0.0196 mu M (S/N = 3). The sensor was also applied for the detection of fenitrothion in tap water. The recoveries for the spiked water samples were between 94.9 and 103.6%. The results mentioned above show that the novel electrochemical sensor is an ideal device for FT determination.