Electrochemical detection of p-nitrophenol (P-NP) using a highly sensitive and selective platform based on single-walled carbon nanotube/pyrenecyclodextrin (SWCNT/PyCD) nanohybrids is described for the first time. The electrochemical performance of the SWCNT/PyCD nanohybrid electrode was fully compared with bare glassy carbon, single-SWCNT, single-PyCD, and SWCNT/CD (without pyrene rings) electrodes. Besides the techniques of cyclic voltammetry and chronoamperometric transients, differential pulse voltammetry (DPV) has been used for the detection of P-NP without any interference from o-nitrophenol (O-NP) at the potentials of -0.80 and -0.67 V, respectively. The SWCNT/PyCD nanohybrid electrode is highly sensitive, and it shows an ultrahigh sensitivity of 18.7 mu A/mu M toward P-NP in contrast to the values reported previously. The detection limit (S/N=3) of the SWCNT/PyCD nanohybrid electrode toward P-NP is 0.00086 mu M (0.12 ppb), which is well below the allowed limit in drinking water, 0.43 mu M, given by the U.S. Environmental Protection Agency (EPA). The analytical performance of the SWCNT/PyCD nanohybrid electrode toward P-NP is superior to the existing electrodes.