Imbibition is one of main production mechanisms in fractured carbonate reservoirs. This mechanism is very dependent on hydrophilicity of reservoir rock and somehow is controlled by it. The contact angle tests, due to the test conditions, i.e, a polished rock section-crude oil droplet system, do not easily indicate the wettability of the porous medium but generally, are accepted to expression of rock wettability. Imbibition tests with a strong dependence on wettability can generalize contact angle tests to wettability of porous medium. Carbonated smart water injection can active water imbibition mechanism and increase production in fractured carbonate reservoirs by wettability alteration to hydrophilic. In this study, the optimal concentration of saline water used with oil in Karanj and Gachsaran reservoirs in Iran was determined by calculating the contact angle in different concentrations and dilutions. Then, the optimal solutions were carbonated by adding carbon dioxide at various temperatures and pressures. The effect of carbon dioxide on wettability of pre-hydrophobized sections was investigated by contact angle experiments. The results show the efficiency of carbonated smart water in wettability alteration as compared with smart water. Then, oil-saturated carbonate plugs were exposed to spontaneous imbibition by optimal solutions in the presence and absence of carbon dioxide. The experiments reveal an increase in oil recovery by imbibition with carbonated smart water. The results of these experiments indicate the water alteration efficiency of carbonated smart water compared with the smart water. A minimum contact angle of 18.75 degrees was obtained by adding carbon dioxide to a smart solution at a concentration of 1000 ppm of different salts and at 10.34 MPa and 75 degrees C. Then, oil-saturated carbonate plugs were exposed to imbibition process with optimal solutions in the presence and absence of carbon dioxide. According to the results of these experiments, oil recovery increased by 78% of the initial oil in place by imbibition in the presence of carbonated smart water.