Recently, many researchers have focused on the usage of electromagnetic waves in oil production and well stimulation, but so far the effect of these waves on the fluid and rock interaction and its simultaneous effect with nanoparticles have not been investigated. Fluid-rock interaction is one of the most important factors affecting fluid distribution in the reservoirs. In this study, the oil reservoir rock wettability alteration under electromagnetic heating and the presence of nanoparticles has been investigated. Three nanoparticles of TiO2, Fe3O4, and TiO2/Fe3O4 have been utilized. TiO2 nanoparticles are commercially available, and the other mentioned nanoparticles are synthesized via a co-precipitation method. Citric acid has been used to modify surfaces of nanoparticles and stabilize them in water as the base fluid. Also, the adsorption of the nanoparticles on the rock surface has been determined. In the next step, the amount of oil outflow from the rock has been measured and reported as the external fluid imbibition. In this process, the nanoparticle performance in wettability alteration was investigated using pH and inductively coupled plasma (ICP) analyses. To better understand the governing mechanisms, oil viscosity was measured by mixing the oil with nanoparticles and put under irradiation. The results reveal that the microwave has a great ability to reduce oil contact angle with carbonate rock. In the presence of 0.2 wt% Fe3O4 nanoparticles, the contact angle was reduced from 155° to 19° after 28 min of irradiation, indicating strong rock hydrophilicity. Furthermore, microwave irradiation on Fe3O4 nanofluid extracts 75% of the oil from the rock. With microwave radiation, the pH of the nanofluid increases and hence, more nanoparticles are adsorbed on the rock which subsequently causes more rock dissolution. The viscosity change results prove that there is an optimal irradiation time of 5 min in which oil viscosity reduces from 481 cP to 410 cP and then increases to 827 cP. Moreover, the application of further nanoparticles diminishes the oil viscosity at optimum irradiation time in which Fe3O4 has the most oil viscosity reduction, representing 481 cP to 200 cP at 50% microwave power level.