In this research, we synthesized mono-substitued derivatives of dieckol which has many phenolic OH groups. By developing condition to react only one of them, we obtained the mono-substitued derivatives through O-benzylation and O-methylation. Using dimethyl sulfate and specific condition, we selectively O-methylated to one hydroxyl group to synthesize 9”-methoxy dieckol. In the same method, we react benzyl bromide to same the hydroxyl group to synthesize 9”-benzyloxy dieckol. All products and structures are confirmed by 1H-NMR, 13C-NMR, 2D-NMR and the other techniques.