In our continuing search for biologically active compounds from edible brown alga, Eisenia arborea was examined. Here we report the progress on the purification, biological activities and structural determination of the purified compounds. From the 100% methanol extract of Eisenia arborea, solvent partition fractions were prepared by using n-hexane(EAH), chloroform(EAC), butanol(EAB) and water(EAW). Among them EAB showed strong anti-oxidative, AChE* and BuChE** inhibitory and anti-tyrosinase activities. The EAB of Eisenia arborea showed 81.3% DPPH radical scavenging activity, 83.1% AChE inhibitory activity, 99.5% BuChE inhibitory activity and 75.3% tyrosinase inhibitory activity at 100 ppm. Using a series of ODS open column chromatography, four purified fractions, EAB-5, EAB-6 and EAB-8, EAB-9, could be obtained. At 100 ppm, they showed anti-oxidative activity as 72.1, 76.8, 67.5, 74.0%, anti-tyrosinase inhibitory activity as 66.3, 67.85, 91.3, 87.3% , and AChE inhibitory activity as 96.23, 98.99, 97.20, 96.07%, and BuChE inhibitory activity as 95.5, 97.9, 97.6, 98.0%, respectively. The major compounds of the purified fractions of EAB-5, EAB-6 and EAB-8, EAB-9 were determined by ¹H and ¹³C NMR and MS analysis. The compound EAB-5 and EAB-6 was turned out to be eckol whereas the compound from EAB-8 was turned out to be dieckol, respectively. The major compounds from EAB-9 are also to be discussed. *AChE : Acetylcholinesterase **BuChE : Butyrylcholinesterase