The molecular mass of the purified killer toxin from the marine killer yeast YF07b was estimated to be 47.0 kDa. The optimal pH and temperature of the purified killer toxin were 4.5 and 40 degrees C, respectively. The toxin was activated by Ca2+, K+, Na+, Mg2+, Na+, and Co2+. However, Fe2+, Fe3+, Hg2+, Cu2+, Mn2+, Zn2+, and Ag+ acted as inhibitors in decreasing activity of the toxin. The toxin was strongly inhibited by phenylmethanesulphonyl fluoride (PMSF), iodoacetic acid, ethylenediaminetetraacetic acid, and 1,10-phenanthroline. The Km of the toxin for laminarin was 1.17 g L-1. The toxin also actively hydrolyzed laminarin and killed the whole cells of the pathogenic yeast in crab.