A direct analytical technique was developed and tested for correct estimation of recovery of Eco-elements such as Li, B, Br, in the seawater, and three processed seawaters from Hanjoo Co. Ltd. The reliability of recovery technique and the correct estimation of total recoveries become a major interest before the launch of pilot plant. High matrix solutions are frequently affected in analyte response during instrumental analysis as the concentration of major component changed drastically. To overcome such a complication during standard sample preparation and a better application in pilot plant, a modified matrix matching standard addition method was developed and the reliability was checked. The detection limit of elements in several seawaters analyzed by applying the modified matrix matching standard addition method were 0.144 – 0.258-g/dm3 for lithium, 0.0.013 – 0.18mg/dm3 for boron, and 4.23 – 17.8mg/dm3 for bromine. The instrumental analysis was carried by AAS for lithium and ICP-AES for boron and bromine.