Bacterial isolation is crucial for elucidating the algal-lytic effects of algicidal bacteria and their practical application in controlling cyanobacterial blooms. In this study, algicidal bacterium Acinetobacter sp.R14 was isolated from surface water of Lake Taihu by oligotrophic method. It was found that without extra nutrition addition, the inoculation of Acinetobacter sp.R14 at a final cell density as low as 7.5×10³ CFU mL^-1 could still cause Microcystis aeruginosa 9110 cells to decline by 97.95% within 7 days. This is the first report that a bacteria with algicidal activity was identified as genus Acinetobacter, and the characteristics of high algicidal efficiency at a low cell density and organic carbon concentration may suggest that the oligotrophic method is a useful strategy to isolate high effeciency algicidal bacteria. It was demonstrated that the cyanobacterial cells were killed by the combination of direct and indirect attack of Acinetobacter sp.R14, and the extracellular compounds secreted had a relative stability towards the change of temperature and pH. With strong algicidal activity in conditions close to natural water environment, Acinetobacter sp.R14 can be used as a potential agent for controlling dominant cyanobacteria species in Lake Taihu.