Large-scale and vertically aligned nitrogen-doped carbon nanotubes were synthesized by pyrolysis of pyridine with ferrocene as the catalysts under either pure NH3 or a mixture of NH3 and argon atmosphere using injection chemical vapor deposition method. Nitrogen content ranges from 4.8 at. % to 8.8 at. % and changes as a function of growth temperature and the flow rate of NH3. NH3 not only increases the nitrogen content of carbon nanotubes but also increases the proportion of pyridine-like N doping in the carbon nanotubes. It suggests that nitrogen concentration and nitrogen doping environments of carbon nanotubes could be controlled by changing the growth temperature or flow rate of NH3.