In the present study, antimicrobial activities of multiwalled carbon nanotubes (MWCNTs) functionalized with ethanolamine (EA) groups were investigated. Therefore, MWCNT were first functionalized with mono-, di-, and triethanolamine (MEA, DEA, and TEA) under microwave technique. Development of functional groups on the MWCNT surface was confirmed by Fourier transform infrared and thermogravimetric analysis. Morphological variation was investigated by transmission electron microscopy. Then, antimicrobial activities of pristine and functionalized MWCNT (MWCNT-MEA, -DEA, and -TEA) were tested against different bacteria species. The studies have been done on four Gram-negative bacteria (Escherichia coli, Klebsiella pneumonia, Pseudomonas aeroginosa, and Salmonella typhimurium) as well as four Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus, Bacillus cereus, and Streptococcus pneumonia). The results based on minimal inhibitory concentration and radial diffusion assay were shown that the antimicrobial activity of MWCNT-TEA > MWCNT-DEA > MWCNT-MEA > pristine MWCNT. Based on the results, it seems that EA groups could play an important role in antimicrobial activity of MWCNT. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 1774–1781, 2014.