An agar-degrading marine bacterium, strain AS-3 was isolated from the seawater. The strain AS-3 was identified as Algibacter lectus AS-3 by 16S rDNA sequence. The optimum medium for agarase activity of the isolated strain was determined to be marine medium, marine broth 2216 containing 0.1% agar as carbon source. An extracellular agarase was purified 6.9-fold from the culture supernatant by ammonium sulfate precipitation, ion exchange chromatography and gel filtration methods. The optimum pH and temperature for this enzyme were 7.0 and $40-50^{circ}C$, respectively. Antioxidative activity of the strain AS-3 was 62.4% in the supernatant cultured for 12 h.