This work reports a simple and one pot synthesis of water dispersible l-cysteine stabilized silver nanoparticles (l-CYS-AgNPs) in an acidic media. Silver nanoparticles were synthesized within few minutes of reaction time (< 5 min) at room temperature without needing to heat and use of any hazardous organic solvents. Prepared nanoparticles were characterized by UV-Visible spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction and zeta potential analysis, respectively. Surface plasmon resonance band of AgNPs which was observed at 392 nm by UV-Visible spectroscopy indicated successful formation of l-CYS-AgNPs in acidic media. Imaging techniques showed that AgNPs possess spherical morphology and average size of 25 nm. Nanoparticles were stable for more than 2 months when stored at ambient temperature. This approach is a facile and rapid one pot synthesis which can be stored as a homogenous aqueous dispersion for more than 2 months. Being stabilized by a sulfur-containing amino acid (l-cysteine) and the synthesis carried out in a moderately acidic media (pH 5.3) are distinctive aspect of this work. These stable l-CYS-AgNPs could be used as a catalyst and sensor applications for advanced perspective against water pollution and industrial effluents.