A new cyclic decapeptide, trikoramide A (<b>1</b>), has been isolated from samples of the marine cyanobacterium <i>Symploca hydnoides</i>, collected from Bintan Island, Indonesia. Trikoramide A (<b>1</b>) is a C-prenylated cyclotryptophan-containing cyanobactin. Its planar structure was deduced by 1D and 2D NMR spectroscopy as well as HR-MS/MS data. In addition, its absolute configuration was determined by Marfey's method and 2D NOESY NMR spectroscopic analysis. Compound <b>1</b> possessed cytotoxicity against the MOLT-4 and AML2 cancer cell lines with IC<sub>50</sub> values of 4.8 and 8.2 μM, respectively.