Epidermal growth factor (EGF) family is proposed to be a negative regulator for neocortical development, such as GABAergic development. We previously found that EGF as neonate down-regulates AMPA-type glutamate receptors in the parvalbumin (PV)-positive GABAergic neurons. Here, we investigated the in vivo effects of EGF on the PV immunoreactivity and fast-spiking property of postnatal mice. Western blotting revealed that PV protein levels were down-regulated in both neonatal and juvenile stages. In parallel, PV-immunostaining in the frontal cortex at postnatal 11 days reveals that EGF significantly diminished the frequency of heavily PV-labeled cells, but not the number of total PV-immunoreactive cells. Typically, PV neurons exhibit high frequency discharges of more than 100 Hz without spike frequency adaptation. Thus, we analyzed effects of EGF on the fast-spiking property. At postnatal 4 weeks, the maximum frequency to a higher injected current (i.e., +1 nA) was diminished by EGF administration, though the frequency triggered by lower currents was not affected. Concomitantly, the protein level of voltage-gated potassium channel, Kv3.1, was down-regulated to ~80 % of control. Thus, EGF attenuates the acquisition of neurochemical phenotype and fast-spiking property of PV neurons during postnatal development.