Recently, nanoparticles have been used along with surfactants for enhancing oil recovery. Although the recent studies show that oil recovery is enhanced using nanoparticle/surfactant solutions, some effective parameters and mechanisms involved in the oil recovery have not yet been investigated. Therefore, the temperature effect on the stability of nanoparticle/surfactant solutions and ultimate oil recovery has been studied in this work, and the optimal concentrations of both SiO2 nanoparticle and surfactant (sodium dodecyl sulfate) have been determined by the Central Composite Design method. In addition, the simultaneous effects of parameters and their interactions have been investigated. Study of the stability of the injected solutions indicates that the nanoparticle concentration is the most important factor affecting the solution stability. The surfactant makes the solution more stable if used in appropriate concentrations below the CMC. According to the micromodel flooding results, the most effective factor for enhancing oil recovery is temperature compared to the nanoparticle and surfactant concentrations. Therefore, in floodings with higher porous medium temperature, the oil viscosity reduction is considerable, and more oil is recovered. In addition, the surfactant concentration plays a more effective role in reservoirs with higher temperatures. In other words, at a surfactant concentration of 250 ppm, the ultimate oil recovery is improved about 20% with a temperature increase of 20 °C. However, when the surfactant concentration is equal to 750 ppm, the temperature increase enhances the ultimate oil recovery by only about 7%. Finally, the nanoparticle and surfactant optimum concentrations determined by Design-Expert software were equal to 46 and 159 ppm, respectively. It is worthy to note that obtained results are validated by the confirmation test.