The laser ablation techniques was employed to prepare TiO2 nanoparticles by pulsed laser ablation of titanium target immersed in the double distilled deionized water using wavelength of 532nm and 1064nm of Nd:YAG laser with energy 500mJ. The as prepared products werecharacterized by X-Ray diffraction (XRD), Atomic Force Microscope (AFM) andUV-Vis spectrophotometer. The results indicate that the Tio2 nanoparticles are synthesized at room temperature and the average diameter is about (84.78, 95.96) nm to the wavelength (1064nm, 532nm) respectively. The optical study shows the nanoparticles possesses direct optical transition with band gab (3.82,3.65)to the wavelength(1064nm,532nm) respectively.Aheterojunctionphotodetectorfabricatedby drop cast film of colloidal TiO2NPs(nanoparticles) onto p-type single crystalsilicon wafer.I-V characteristics of Tio2NPs/Si heterojunction under darkand illumination conditions have been studied.