Abstract: This research investigation the effect of Ag nanoparticle to improvement the sensitivity of photodetector. Porous silicon prepared with photoelectrochemical etching by using n-type silicon substrate. To increase the efficiency of detection deposited the Ag nanoparticle on porous silicon surface by annealing process. SEM and AFM technique were used to study the morphological characteristics of the PSi surface. Dark and photo current-voltage and responsivity were probed before and after the deposit Ag nanoparticle and the responsivity increased from 0.35-0.6 A/W.