An alternative chemical vapor doping (CVDo) method for doping transparent and conductive films of carbon nanotubes (CNTs) is presented. The different effects between the traditional solution doping process and the proposed vapor doping method are compared in detail by means of optical microscopy, SEM, sheet resistance measurements, and Raman and UV–Vis–NIR spectroscopy. It was shown that the level of reduced sheet resistance was comparable for the two treatments but the vapor-treated film displayed better stability in air as well as other significant advantages that include its appropriateness for different types of flexible substrates. A mechanism for chemical vapor doping is proposed.