The water injection is one of the common methods of enhance oil recovery. This process may be more efficient by using nanofluids injction instead of water. Nanoparticle may change the physical properties of water to attain more oil production. In this study a mathematical and numerical model is developed to analyze the enhancement of oil recovery into the porous medium by using silica/water nanofluids. the results clearly show that , water saturation is significantly increased in porous core by adding a low concntration of silica nanoparticle into water. In addition, the oil recovery rises considerably.