The Cenomanian (Upper Cretaceous) Maha Sarakham Formation of the Khorat Basin, northeastern Thailand consists of three evaporite units (Lower, Middle and Upper Salt) interbedded with clastic sediments and exhibits abundant deposits of potash. Although numerous studies have been carried out on the Khorat potash deposit, results are still equivocal with regard to the origin of the rock salt, whether it was marine or non-marine (hydrothermal and/or mixed fluids). The purpose of this study is to examine the origin of rock salt based on elemental compositions and boron isotope analyses in the southwestern part of the Khorat Basin. A stratigraphic correlation of five boreholes (K-201– 205) located in Bamnet Narong and Chaturat districts, Chaiyaphum province, Thailand, revealed a salt dome structure. The elemental composition and δ¹¹B values in the longest borehole K-203 indicate a precipitation of halite and carnallite from seawater. Rare earth elements (REE) of claystone and siltstone from five boreholes (K-201– 205) are comparable to the REE of sandstone from the Simao Basin in China, which suggest a similar provenance. Stratigraphic comparisons and geochemical signatures are important for a better understanding of the recharge models of paleoseawater. In agreement with some previous studies, we conclude that the Cenomanian evaporites within the Khorat Basin are marine deposits.