Abstract-Ten new antifouling briarane diterpenoids, juncins R-ZI (1-10) were isolated from the South China Sea gorgonian coral Junceella juncea. The structures of these new compounds were established by extensive spectroscopic analysis, including 1D and 2D NMR data. Compounds 1-10 all showed potent antifouling activities against the larval settlement of barnacle Balanus amphitrite at nontoxic concentrations with EC 50 values of 0. 004, 0.34, 2.65, 1.61, 3.77, 21.06, 0.004, 0.14, 1.47, and 0.51 mg mL À1 . The structure-activity relationship was discussed.