A bacterial strain N29 was isolated from the sediment of Mirs Bay during Scrippsiella trochoidea bloom. By analysis of its morphology and biochemistry, as well as homology screening using 16S rRNA gene sequences, strain N29 was identified as Bacillus anthracis CEB95-0033. Strain N29 showed algicidal activities against S. trochoidea and Prorocentrum micans but had no effect on Skeletonema costatum and Phaeodactylum tricornutum. Moreover, the algicidal activity correlated with bacterial concentration, algal species and incubation period. More specifically, strain N29 had little algicidal effect at low volume fraction of 0.1% and 1% for S. trochoidea and P. micans, because of the densities of S. trochoidea and P. micans increased substantially just like the controls in the incubation period. However, after incubation of strain N29 with S. trochoideaat volume fraction of 1% and 2%, 100% of S. trochoidea cells were killed within 120 h and 96 h. Further, algicidal effect of strain N29 on P. micans required higher bacterial concentrations. For example, at 5% volume fraction, 85% of P. micans cells were killed within 120 h; at 10% volume fraction, 100% of P. micans were killed within 72 h. It showed that strain N29 had algicidal effect on S. trochoidea and P. micans in shorter incubation time with higher bacterial concentration. In addition, algicidal effects were checked with bacterial culture filtrates and heated filtrates of strain N29 on S. trochoidea or P. micans, which showed that they lysed P. micans but been ineffective on S. trochoidea. It implied that strain N29 killed P. micans by releasing some heat-tolerant algicide, but killed S. trochoidea via direct attack or competition for nutrients.