One of the most common methods for preventing scale formation is through the use of scale inhibitor. This study was conducted to investigate the permeability reduction caused by deposition of barium sulfate in Malaysian sandstone and Berea cores from mixing of injected Malaysian seawaters (Angsi and Barton) and formation water that contained high concentration of barium ion at various temperatures (50–95°C) and differential pressures (75–200psig). Scale inhibition efficiency was determined in both the bulk jar and core tests by using scale inhibitors Methylene Phosphonic Acid (DETPMP), Poly-Phosphino Carboxylic Acid (PPCA), and Phosphonate-based scale inhibitor (PBSI) at various temperatures (50–95°C) and concentrations. The results showed that a large extent of permeability damage was caused by barium sulfate that deposited on the rock pore surface. At higher temperatures, the rate of BaSO 4 precipitation decreases since the solubility of BaSO 4 increases with increasing temperature. At 60°C temperature, PPCA showed very efficient BaSO 4 inhibition effect where it reduced most amount of BaSO 4 compared to the DETPMP and PBSI inhibitors.