A sensitive and selective electrochemical sensor based on Au-TiO2 nanoparticles/Chitosan/gold (Au-TiO2 NPs/Chit/gold)-modified electrode was developed for the detection of mercury ions (Hg2+), in which the composite electrode was synthesized via sol-gel method and followed by a self-assembly strategy. The morphology and microstructure of the Au-TiO2 NPs are characterized using transmission electron microscopy and X-ray diffraction. The results demonstrate the presence of a monolayer of well-dispersed Au-TiO2 NPs with an average size of 5-15 nm. The electrochemical properties of the resultant Au-TiO2 NPs/Chit/gold-modified electrode and its response to Hg2+ are studied using cyclic voltammetry and differential pulse anodic stripping voltammetry. The operational parameters that influence the deposition and stripping, such as the supporting electrolytes, pH value, deposition potential and deposition time, are carefully studied. Under optimal conditions, the as-prepared Au-TiO2 NPs/Chit/gold-modified electrode exhibits a wide linear response range of 5.0-400.0 nM with a correlation coefficient of 0.999. In addition, the limit of detection is 1.0 nM with a 240 s preconcentration (S/N = 3), which is lower than the World Health Organization and Environmental Protection Agency limits for Hg2+. The practical application of the proposed method is evaluated in a real water sample, and good results are obtained. This finding is potentially important for electrochemical sensors in environmental applications.