We have described the development of electrochemical nano sensor for the detection of mercury ions from aqueous solutions based on the formation of polyaniline nanoparticle films. Screen printed carbon electrodes were modified with polyaniline nanoparticles. Electropolymerization of polyaniline nanoparticles was performed by the pulsed potentiostatic method. The sample of polyaniline nanoparticles was prepared by repeating the potential step process three times. Structural and morploigcal characterization of polyaniline nanoparticles modified screen printed carbon electrode was performed using Fourier Transmission infrared (FTIR), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). PANI nanoparticles were spherical shaped having an apparent dimeter varying from 20 to 45 nm. Square wave anodic stripping voltammetry was used for the detection of Hg(II) on PANI NPs modified screen printed carbon electrode under optimized conditions. Hg(II) was deposited for 60 seconds by the reduction of Hg(II) in buffer solution:(citric acid and sodium chloride pH 2.30), followed by Hg stripping between 0.3 and 0.8 V at the following parameters: Scan rate: 100 mV s-1, frequency: 60 Hz, amplitude: 0.025 V and increment: 4.0 mV. it was found that the PANI NPs modified screen printed carbon electrode had a highest anodic stripping peak current in solution of pH 2.30. The limit of detection value for Hg(II) was found to be 2.50 ± 0.03 ppb. The limits of detections determined are below the corresponding guideline value from the World Health Organization (WHO). In addition, the modified nano electrode exhibited excellent reproducibility and high stability. The developed method was successfully applied to determine Hg(II) in real water samples with satisfactory results.