Abstract: An ultrasound-assisted process for magnesium (Mg²⁺) extraction from metallurgy wastewater was developed using dinonyl naphthalene sulfonic acid. Effects of extractant concentration, immersion depth of ultrasonic horn, extraction time, ultrasonic power and the volume ratio of organic phase and aqueous phase (O/A) on Mg²⁺extraction were investigated. The results show that ultrasonic-assisted extraction can decrease extraction time and improve extraction speed for 20 times. The optimal process parameters are:25℃, extractant concentration=0.8 mol·L^-1, immersion depth of ultrasonic horn=5 mm, ultrasonic extraction time=2 minutes, extraction power=108 W and O/A ratio=3:1. UV spectrophotometry analysis shows that ultrasonic irradiation does not destroy the structure and performance of the extractant which can be reused after regeneration. Therefore, the ultrasonic-assisted process is beneficial for continuous Mg²⁺ extraction and improves productivity.