A nano-second pulsed laser processing has been normally conducted with laser induced plasma, which leads to the reduction of laser energy absorbed to a specimen. Therefore, material removal characteristics are strongly affected by phenomena of laser induced plasma. It is considered that plasma generation is affected by pulse duration and laser intensity. However, influence of laser parameter on plasma generation has not been sufficiently clarified yet. In this study, the influences of pulse duration and laser intensity on plasma were investigated by measurements of plasma size and transmittance of laser energy through plasma. Finally, effective energy to material and removal characteristics were discussed with calculated actual laser energy absorbed to a specimen.