Matrix metalloproteinases (MMPs) regulate angiogenic processes essential for tumor growth and metastasis, and MMP-2 inhibitors are expected as antimetastatic and antiangiogenic agents. In our search for MMP inhibitors from Japanese marine invertebrates, we found that the hydrophilic extract of the marine sponge Agelas nakamurai significantly inhibited MMP-2. Bioassay-guided isolation afforded a fluorescent alkaloid ageladine A (1). We report the isolation, structure elucidation, and antiangiogenic activity of this new alkaloid. The molecular formula of ageladine A was established as C₁₀H₇N₅Br₂ (containing two bromine atoms) via HR-FABMS and NMR data. Its structure was determined as 4-(4,5-dibromo-1H-pyrrol-2-yl)]-1H-imidazo[4,5-c]pyridin-2 amine through 2D NMR analysis and studies of N-methyl derivatives (2-4). Ageladine A inhibited MMP-2, -1, -8, -9, -12, and -13 with IC₅₀ values of 2.0, 1.2, 0.39, 0.79, 0.33, and 0.47 µg/mL, respectively. Unlike typical MMP inhibitors, it did not chelate Zn²⁺ and showed non-competitive inhibition of MMP-2. Antiangiogenic effects included inhibiting bovine aortic endothelial (BAE) cell migration (33.3% at 5 µg/mL, 65.9% at 25 µg/mL) and suppressing vascular formation in a mouse embryonic stem (ES) cell in vitro model at 10 µg/mL. Ageladine A is the first bromopyrrole alkaloid from Agelas spp. to contain a 2-aminoimidazolopyridine moiety. With its fluorescent properties and bioactivity, it holds potential as a bioprobe for studying angiogenesis.