Graphite pencil lead (GPL) covered with Au nanodendrites (AuNDs) (the AuND@GPL sensor) has been demonstrated as an electrochemical sensor for simultaneous detection of Pb(II), Cu(II) and Hg(II) in water samples. To meet both the demands of cost-effectiveness and required analytical performance, a cheap GPL was chosen as a sensor platform and AuNDs providing a large electroactive surface area were fabricated on the surface of GPL by a simple electrodeposition in less than one minute. Due to the incorporation of AuNDs, the sensitivities of simultaneous detection of Pb(II), Cu(II) and Hg(II) were improved with a limit of detection below 0.2ppb, and the peak intensities did not vary significantly even though concentrations of interferants were 100-fold greater. The sensor-to-sensor reproducibility was good (relative standard deviation below 4.6%), which is mainly contributed to the simple one-step electrodeposition for sensor preparation. The overall detection performance was better or similar in comparison with those of previously reported GPL-based sensors. Moreover, when real lake water samples were analyzed, the AuND@GPL sensor was able to accurately determine the Pb(II), Cu(II) and Hg(II) concentrations. The sensor is cost-effective due to the use of GPL as a platform, so it has a strong potential as a disposable electrochemical sensor for at-site water quality monitoring. [GRAPHICS] .