We firstly demonstrated the detection of anions in air using a nano field-effect transistor (nanoFET) device. Negative ions in air charged the top surface of the silicon nanoFET channel affecting the fieldeffect and making a conductance change of the channel proportional to anion concentration around the nano channel sensing surface. The real-time detection of anions in air with the nanoFET was performed for various anion concentrations which were differentiated by the distance of the anion generator to the nanoFET sensor. The air anions detection characteristics of the nanoFET device were evaluated with sensitivity and conductance change rates analysis.