Many efforts have been made for developing effective anti-fouling agents for practical use, but were in vain so far. In order to search for a new anti-fouling compound, we tried to find it from microbial secondary metabolites using inhibitory activity against carbonic anhydrase (CA) in the striped barnacle (Balanus amphitrite) as an index, because CA is essential for growth through calcification of barnacle exoskeleton. One effective compound was discovered from culture filtrate of Streptomyces eurocidicus mf294 after screening a total of 692 strains of mold and actinomycetes and purified. This compound was identified as 2-nitroimidazol (2-NI), which had been previously identified as an antibiotic named azomycin. 2-NI showed growth inhibitory activity to the striped barnacles at 10 ppm in the lab test. Then, we tried to test 2-NI for anti-fouling activity in natural seawater, but could not get any successful results.