Difficulties and constrains of water & gas injection, like unfavorable mobility ratio, gravity override and underride, and early fingering of injected fluid have led to application of water alternating gas (WAG) injection method instead of water flooding. Nanotechnology can be applied to enhance the performance of WAG process by changing microscopic and macroscopic sweep efficiencies of the process. In this study, several experimental works have been completed to investigate the improvement of the efficiency of the WAG method by application of nano-particles in the aqueous phase. The developed water-based nano fluid alternating gas injection effects on the oil recovery were studied by different core flooding tests in carbonated samples and the results were compared to the conventional WAG approach. The medium crude oil sample and plugs were provided from a mature oil field in the Middle East. Silica nano-powder (SiO2) with particle size of 11-14 nm was used to prepare the water-based nano fluid. Several characterization experiments such as Interfacial tension (IFT) and contact angle measurements were performed to study the influences of the new method on the IFT and wettability alteration during flooding. Experimental results demonstrated more than 20% incremental in recovery factor by Nano-WAG process in comparison to the WAG process. Our study showed that adsorption of SiO2 nano particles on the rock surface changed the wettability of the rock from the oil wet to strongly water wet which affects the recovery. In addition, reduction of IFT occurred due to the placement of nanoparticles on the interface of oil and water phases. Our experiments indicated that water-based nano fluid alternating gas injection is a novel potentially feasible process for enhanced oil recovery and can be used in the field applications to overcome the problems of the WAG and enhance the oil recovery.