In this work, synthesis and characterizing of carbon: selenium nanoparticles (C:Se NPs) are synthesized by laser ablation Q-switched Nd:YAG laser with wavelength of 1064 nm at different laser pulses energy 200, 600 and 800 mJ with 100 shots and porous silicon (PS) was presented. X-ray diffraction (XRD) was utilized for examining the structural properties. In addition, the results of the Atomic force microscope (AFM) analysis an 39.76 nm as average diameter which is coordinated in rod-like shape appearing for C:Se NPs, also the transmission electron microscope (TEM) indicated that the synthesized C:Se particles have been spherical with average particle size in range of (25 and 75) nm. Lastly, the variations of operation temperature related toNH3 and NO2 gas sensors that are fabricated from prepared samples on the sensor sensitivity, recover time and response time were examined, the maximum sensitivity is approximately 205% with regard to (C:Se NPs) ablated via laser energy 800mJ on PS of gas NO2, also the maximum sensitivity is approximately 43% in terms of(C:Se NPs) ablated via laser energy 200mJ on PS of gas NH3.