In recent years Low Salinity Waterflood (LSW) had been supposed as trusty method to improve oil recovery and the most essential aspect is a alteration of divalent ion concentration in reservoir pore volume as a respon LSW. The objective of this paper are to find divalent diffusivity constant (Ca2+ and Mg2+) in berea sandstone by ionsmass conservation equation along with Atomic Absorption Spectroscopy (AAS) as validation. The study was conducted at 2 berea core having porosity : 0.235 and 0.230 and permeability : 661 mD and 550 mD, we use synthetic formation water accordance to "LN" field property. Experiment was treated by by diluting Ca2+ up to 79% from its original value and by diluting Mg2+ up to 95% from its original value while other ion were maintained fit to their original value. As a result we got difusion constant 0.0620 cm2.min-1 and 0.2667 cm2.min-1for Ca2+ and Mg2+, respectively.