Marine algae Gelidium, Grateloupia elliptica Holmes, and Codium fragile are employed for preparation of PANI/seaweed composites. Infrared absorption (IR), electron spin resonance (ESR) spectroscopy measurements are carried out to confirm the resultant structure. The direct use of natural biological materials for polymerisation reaction allows us to production of polymers with characteristic surface. This can be referred to as bio-interface polymerisation.