Influences of gases on the field emission were measured using the specimens of Spindt‐type Mo field emitter array. Gases were introduced into a vacuum chamber where the specimens were driven with pulse and dc voltages to emit electrons. In case of pulse drive, effects of N2 , H2 , Ar, or CO2 on emitter arrays could hardly be observed until the vacuum level reduced to 5×10−6 Torr. When the vacuum level was recovered to the background level, emission showed the recovery to be almost the same value as that before gas introduction. When pulse driven, a small amount of H2 gas reduced the work function of the emitter surface and increase the emission characteristics of emission array. In case of dc drive, on the other hand, emission began decreasing at 10−7 Torr. The introduction of SO2 led to the decrease of emission to ∼70% of the initial value at 5×10−6 Torr because of the contamination of emitter tips caused by SO2 when pulse driven. It was also clarified that CH4 , H2 , and CO adsorbed to emitters to reduce the work function of emitter tips. Particularly with CH4 , emission was doubled or more the initial value at 5×10−5 Torr.