Many efforts have been made to develop novel electrochemi-cal biosensor with good sensitivity. A signal amplification strategybased on nicking endonuclease (NEase) has attracted more andmore attentions because of the simple detection process and high selectivity toward environmental Hg2+detection over otherrelated heavy metal ions [29–32]. The NEase can recognize spe-cific sequence in duplex DNAs and nick only one specific strandof the duplex [33]. In this work, a novel, selective, and sensitiveelectrochemical method based on NEase-catalyzed signal ampli-fication was developed to detect Hg2+. The signal amplificationwas achieved by the recycling of Hg2+and probe B. The detec-tion limit of this electrochemical biosensor using this method was8.7 × 10−11M. The electrochemical biosensor exhibited high sen-sitivity. Herein, we evaluate the performance of this novel assayand show that Hg2+can be detected down to the EPA-acceptableconcentration (10 nM) in drinkable water.