Algaecide treatment is a management strategy to control cyanobacterial blooms. This study assessed three oxidizers such as hydrogen peroxide (H₂O₂), potassium ferrate (K₂FeO₄) and sodium percarbonate (Na₂CO₄), on mitigating cell numbers and inhibiting the photosynthetic activity of cyanobacteria colonies collected from natural lake. Addition of those three algaecides could disrupt cyanobacteria cells and inhibit the maximum (F_v/F_m) and actual (F_v'/F_m') quantum yield of cyanobacteria, and the inhibitory effect was enhanced when the concentration of algaecides increased. Cyanobacteria cells tended to be more sensitive to H₂O₂, in comparison with other two algaecides. In addition, H₂O₂ decomposed more rapidly, and mitigating efficiency as well as the inhibitory effect of photosynthetic activity declined when cyanobacteria biomass increased. When the initial cell density was 10and 100μg/L, the inhibition rate of 5mg/L H₂O₂ on the maximum quantum yield of cyanobacteria was 10% and 1%, while the degradation rate was 64.9% and 97.5%, respectively. These results indicated that using H₂O₂ for cyanobacterial bloom control should be exerted when cyanobacteria biomass is relatively low, since the low dosage could function well at the early stage of cyanobacterial bloom.