Background & Objectives: Zero-valent iron nanoparticles have been widely used as an effective agent in environmental remediation. The present study was designed to determine bactericidal effect of stabilized zero-valent iron nanoparticles on E.coli. Methods: Nano zero-valent iron (NZVI) particles were synthesized and characterized using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Carboxymethyl cellulose (CMC) was used for stabilizing particles. Inactivation of E.coli was tested using different wt% (w/w) of CMC and different concentrations of stabilized nanoparticles for a period of 30 min. To compare antibacterial effects of stabilized and non-stablized NZVIPs, 0.1g/l of nanoparticles was mixed with E. coli suspension. For statistical purposes three-way ANOVA and Duncan's tests were used. Result: Increasing nanoparticle concentration and contact time increased E. coli inactivation efficiency. However bactericidal effect was decreased with increasing wt% of NZVI stabilizer. Significant differences were observed between concentrations of 1 and 2 g/l and 0.1 and 0.5 g/l for all levels of bacteria density and CMC except for 0.02 wt%. Efficiency of 100% was obtained at concentrations of 1 and 2 g/l. Significant differences were found between results of stabilized and non-stabilized nanoparticles. After contact time of 120min, inactivation efficiency of 100 and 78% were observed for non-stabilized and stabilized particles, respectively. Conclusions: CMC might prevent direct physical contact of bacteria with nanoparticle’s surface and reduce their interaction and consequently cause a reduction in toxicity of nanoparticles against bacteria.