Several studies have confirmed positive effect of low salinity water injection on Enhanced oil Recovery (EOR). Although more than 60 percent of oil reservoirs around the world are carbonate reservoir, but most of these studies have done on sandstone reservoirs. However, effect of low salinity water injection on carbonate reservoirs has attracted more attention in recent years. In this study, at first, optimum salinity level of 10 times diluted seawater was discovered by spontaneous imbibition experiments on limestone cores. Then, experiments were conducted using dolomite slabs in the optimum salinity level and attempts were made for evaluating governing mechanisms in low salinity water injection based on wettability alteration measurements. According to results obtained from these experiments, Ca 2+ and Mg 2+ cations were determined as main factors and sulfate, nitrate and hydroxide anions were determined as facilitating factors of wettability alteration toward more water wetness. Best results obtained with wettability index (WI) of 0.88 in using a solution consist of Ca 2+ , Mg 2+ and SO 4 2- ions. By adding bicarbonate ion to this solution (at the same concentration of this ion in 10 times diluted sea water) WI decreased to 0.59, while in two times increasing of salinity level (only by introducing NaCl) WI was reduced to 0.76. This result indicates that bicarbonate ion is a strongly disturbing factor acting against wettability alteration toward more water wetness. Also using a solution consist of Mn 2+ demonstrated that other cations can cause wettability alteration toward more water wetness and enhance oil recovery through surface change mechanism. Also for confirmation of obtained results in contact angle measurement experiments, a triple sequence flooding experiment was done on a dolomite core, that confirmed disturbing effect of bicarbonate ion in EOR. Keywords: low salinity water, carbonate reservoir, enhanced oil recovery, wettability alteration, imbibition, contact angle.