Background: and Objectives:The aim of this study was to detect the antibacterial properties of 0.01, 0.5 and 1% nano-TiO2 and -CdO against E. coli. Materials and Methods: E. coli was cultured in liquid and agar nutrient medium to evaluate the antibacterial effects of 0.01, 0.05 and 1% of both nano-TiO2 and -CdO via the optical density (OD) and log CFU/ml measurements. Results: Non-significant effect was seen for 0.01% of both nano-specimens. While, 0.05 and 1% of both nanoparticles showed considerably decreased bacterial number. A 4.5 and 1.9 times decrease in the OD value was found in the presence of 1 and 0.5% nano-TiO2, respectively(P< 0.001). 1.5 and 3.3 times decreased OD was seen in the presence of 0.5 and 1% nano-CdO, respectively, as compared to control (P<0.001). In the second study, 6.3 log CFU/ml of E. coli were present in the cultures treated with 1% nano-TiO2 and CdO at 4 ºC in water. Control E. coli cells survived for 12 days while complete cell death was seen when 1% nano-TiO2 was applied for 13 hours as compared to 1% nano-CdO, which showed complete cell death after 15 hours. In the third study, E. coli was grown in the agar medium with and without both nanoparticles and suppressed growth (4.5 and 5.6 times; P<0.001) was seen in the presence of 1% nano-CdO and -TiO2, respectively. Conclusion: In spite of the fact that both nanoparticles showed bactericidal activity, nano-TiO2 has proven to be more efficient antibacterial agent as compared to nano-CdO.