Removal of algal blooms in freshwater using magnetic polymer was studied by magnetic field. Results showed that magnetic polymer at optimal loadings (4 mg/Lferroferric oxide modified with 1.6 mg/Lchitosan) could remove over 99% algal cells; meanwhile, the removal efficiency of COD, total nitrogen and phosphorus was found to be 85.0%, 73.9% and 28.7% respectively. Furthermore, effects of ionic strength, pH and cell concentration on the removal of algal cells were analyzed: ionic strength had a negative effect on the removal efficiency which increased with the increase of cell concentration and reached a maximum at pH 7.0.