In both offshore deepwater and shale fields, a large amount of produced water will be generated during field operations. One consequence of significant produced water production from the field is mineral scale formation. Barium sulfate (barite) is one of the toughest scales to manage in oilfield. To combat scale issues, scale inhibitor has been widely adopted to inhibit scale deposition. Previous studies have confirmed that sorptive interactions between chemical inhibitor and scale particles play a vital role in scale prevention and control. Although extensive studies have been carried out on inhibitor-scale interaction, a comprehensive understanding of inhibition is yet available and the detailed sorptive interaction between inhibitor and mineral scale is not fully understood. In this study, experimental efforts have been made to explore the governing mechanism of sorptive behavior of a common phosphonate inhibitor onto the surface of barite particles. Adsorption and desorption experiments involving phosphonate and barite were carried out over a wide range of physiochemical conditions in a systematic manner. It shows that both adsorption and desorption of inhibitor to and from barite surfaces proceed rapidly. At a low phosphonate concentration, surface adsorption mechanism accounts for the interaction between phosphonate and barite. The release of phosphonate inhibitor from the barite surface is controlled by the dissolution dynamics of the formed Ca-phosphonate precipitate. This study is the first report of investigation of barite with phosphonate inhibitor with low and ultra-low concentrations as well as the inhibitory mechanism. The obtained results will improve our understanding of the interaction between phosphonate inhibitors and mineral scale. The findings can provide fundamental information that can benefit the inhibition performance and efficiency for barite scale control in oilfield operations.