Low salinity water flooding is one of the emerging enhanced oil recovery technologies as it has been proven economical and environmentally friendly. However, the recovery mechanism of low salinity water (LSW) is still under debatable due to the complex effect of low salinity water and its ionic compositions. Therefore, this study aims to discover the optimum seawater dilution salinity and influence of single and binary ionic compounds low salinity water on wettability alteration of carbonate core slices at optimum salinity. To achieve that, a modified Design of Experiments (DOE) has been implemented. Contact angle measurement was carried out to characterize the wettability of core slices at 0 hour, after 24 hours and after 48 hours. The results revealed that dilution of seawater reduced the contact angle of carbonate core slices towards more water wet until the optimum salinity of 1750ppm. Further dilution to 700ppm only shown a slight impact in shifting the wettability of the carbonate slices towards more water wet. In single ionic compound LSW, MgCl2 showed the greatest ability in altering wettability. In binary ionic compounds LSW, it was found out that MgCl2 mixed with ionic compounds containing monovalent ion is more effective in altering contact angle than MgCL2 mixed with ionic compounds containing divalent ion which serve as a new finding in current low salinity water study on carbonate rocks. © 2019 Published under licence by IOP Publishing Ltd.