Disruption of controlling impulsivity is an intolerable symptom observed in various psychiatric disorders and could be a risk factor for drug addiction, criminal involvement, and suicide. To elucidate the neurophysiological basis of behavioral inhibition, we recorded single-unit activity in the infralimbic cortex (IL), where is a ventral part of the medial prefrontal cortex, of the rat performing the 3-choice serial reaction time task (3-CSRTT). This task requires the rat to inhibit nose poke responding until a light stimulus is presented briefly in one of three holes. Above 60% (38/56) of isolated IL units were linked to behavioral inhibition. Inactivation of the IL with muscimol (0.1 g/side) disrupted behavioral inhibition in the 3-CSRTT. Furthermore, we employed a 2-choice task (2-CT) which is a more accurate behavioral task in terms of the control of movement. In this task, the rat is required to keep pushing a front panel with its nose until a light stimulus is presented briefly in one of two holes. We first evaluated the pharmacological validity of the 2-CT using nicotine (0.2 mg/kg) and milnacipran (10 mg/kg) that were previously characterized to disrupt and enhance behavioral inhibition in the 3-CSRTT, respectively. Above 30% (14/44) of recorded IL units were linked to behavioral inhibitions in the 2-CT. Most of them showed a transient decline of firing rate immediately before release of behavioral inhibition. These findings suggest that the rat IL plays an important role in inhibition of impulsive behavior.