The effect of hydrazine (N 2H 4) vapor on the properties of single-walled carbon nanotube (SWCNT) networks was investigated by sheet resistance measurement, scanning electron microscopy, Raman spectroscopy, ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy (XPS). Our results show that, even after an auxiliary thermal desorption treatment at 80 °C, the n-doping effect on our SWCNTs caused by N 2H 4 vapor still persistently remained. Further analysis on the XPS data suggests that a reactive chemical species, nitrene (NH), generated during thermal decomposition of N 2H 4, could react with SWCNTs by cycloaddition to form cyclic nitrogen-containing aziridine structures on SWCNTs. Our results also show that the formed nitrogen-containing bonding structures were thermally metastable and could be significantly eliminated upon further annealing at 350 °C. Moreover, it was found that the N 2H 4 vapor treatment could introduce nitroso groups and carbonyl groups, but not carboxyl groups, to our pristine SWCNTs. The mild oxidation could be attributed to the HNO 2 and H 2O 2 produced from the reactions of NH and N 2H 4 with oxygen, respectively, when a N 2H 4 treatment was performed in air.