We present the wall number control of carbon nanotube (CNT) forests grown on metal cat-alyst films in a water-assisted chemical vapor deposition (CVD) by measuring the sheet resistances of metal catalyst films. Catalyst film thicknesses and thickness variations are monitored using a 2-point-based electrical characterization methodology. The electrical characterization and high-resolution transmission electron microscopy analysis showed that single-, double-, and triple-walled CNT forests were grown on iron (Fe) catalyst films with mean sheet resistances of 646.63, 75.40, and 27.84 MX/sq, respectively. The average wall number and outer diameter of CNT forests were found to linearly depend on the log-arithm of the mean sheet resistances of Fe catalyst films.