At present, most oilfields are developed by applying water-flooding technology. However, this technology is often accompanied by inorganic scale deposition on water- and oil-pipe and equipment walls due to the incompatibility between the injection fluid and formation water and for other reasons. Barium and strontium sulfates are highly resistant to the acids that are generally used as scale dissolvers. In this work, a new chelating-agent-based alkaline barium- and strontium-sulfate scale dissolver named SA-209 has been developed. Many of its important parameters such as salt concentration, reaction time, pH value, temperature, etc. that affect de-scaling efficiency are evaluated by experiments and analysis. This dissolver has a high de-scaling rate and low equipment and pipe corrosion, is environment-friendly, and so would have a promising application in oilfields.