New tetraarylboron-ammonium complexes having the general formula: ##STR1## wherein R.sub.1 represents a hydrogen or a halogen atom or a lower alkyl group; R.sub.2 represents a halogen atom or a lower alkyl or a lower alkenyl group; and R.sub.3 represents a heterocyclic amine are provided as active ingredient of anti-fouling paint and also of antiseptic, antifungal agent. These compounds exhibit remarkably long-lasting anti-fouling activities against substantially all kinds of aquatic organisms including slimes with acceptably low toxicity against human beings and also exhibit high antimicrobial activities against various fungi, bacteria and yeasts.