Pseudomonas aeruginosa is a common cause of nosocomial infections and severe infections in burn patients. It is one of the most important extended spectrum β-lactamase (ESBLs) producing bacteria. ESBLs can cause bacteria to resist antibiotics containing a β-lactam group. Problems due to antibiotic resistance have renewed trends toward using silver, because it has bactericidal properties, and there is a significant increase in this property at very low concentrations. Nanosilver in particular, because of its small size and increase in surface/volume ratio compared with bulk silver, makes more contacts with the surrounding space and has more impact on the bacterial environment. In this study, we investigated the antibacterial activity of a nanosilver colloidal (NSC) solution on ESBL-producers and non-ESBL strains of P. aeruginosa using the MIC and MBC methods. The morphology of the bacterial cells was evaluated after treatment with NSC using scanning electron microscopy (SEM). The in vitro cytotoxicity test with the Chinese Hamster Ovary (CHO) cell line was used to evaluate the cytotoxic potential of the NSC solution. The experimental results indicated that 0.312μg ml-1 of NSC could completely inhibit the growth of 107cfu/ml ESBL-producing P. aeruginosa cells in brain heart infusion broth (BHI Broth) and the MBC was determined to be 0.0625μg ml-1. NSC solution in concentrations of 0.03125 up to 0.5μg ml-1 showed no cytotoxicity. It was concluded that NSC solution could be considered as a good candidate for the treatment of infections caused by P. aeruginosa, especially by ESBL-producing strains.