In this paper, the reliability (NBTI degradation: ${Delta}V_{th}$) and device characteristic of nano-scale PMOSFET with plasma nitrided oxide (PNO) is characterized in depth by comparing those with thermally nitrided oxide (TNO). PNO case shows the reduction of gate leakage current and interface state density compared to TNO with no change of the $I_{D.sat};vs.;I_{OFF}$ characteristics. Gate oxide capacitance (Cox) of PNO is larger than TNO and it increases as the N concentration increases in PNO. PNO also shows the improvement of NBTI characteristics because the nitrogen peak layer is located near the $Poly/SiO_2$ interface. However, if the nitrogen concentration in PNO oxide increases, threshold voltage degradation $({Delta}V_{th})$ becomes more degraded by NBT stress due to the enhanced generation of the fixed oxide charges.