Nitrogen-doped single-walled carbon nanotubes (SWCNTs) are synthesized directly on silicon and quartz substrates through a normal chemical vapor deposition (CVD) method. Thermogravimetry mass spectrometry measurements and Raman spectroscopy give firm evidence for framework nitrogen doping. X-ray-photoelectron-spectroscopy analysis further obtains the bonding style of the nitrogen atoms in the carbon framework. The nitrogen doping significantly changes the properties of the SWCNTs. All of the tubes behave like metallic tubes in field-effect transistors. The doped nitrogen atoms introduce a stronger affinity for the SWCNTs to metal nanoparticles. Compared with pristine SWCNTs, the nitrogen-doped tubes show enhanced sensitivity and selectivity for electrochemical detection of some electrophilic species including O-2, H2O2, and Fe3+. They also present improved electrocatalytic activity for oxygen reduction. These unique properties of the nitrogen-doped SWCNTs endow them with important potential applications in various fields.