Abstract: Seven kinds of flocculants, including Aluminium potassium sulfate, aluminum sulfate, calcium hydroxide, ferric chloride, aluminium chloride, polyacrylamide and chitosan were designed to solve the difficulties in harvesting Monoraphidium sp.cells.The results showed that chitosan was the best flocculant.At a dose of 0.04g/L, the microalgal cells were completely flocculating, and had no impairment on the cell integrity.The better concentrations of ferric chloride and aluminium chloride were 0.2 ⁰.4g/L and 0.4 ⁰.8g/L, but higher concentrations restrained the flocculating.The impairment of perric chloride and low concentrations (0.4g/L) of aluminium chloride on the cell integrity could be ignored, but higher concentrations (1.0g/L) of aluminium chloride could destroy the algal cells.The flocculating effect of aluminium potassium sulfate and calcium hydroxide on Monoraphidium sp.cells was relatively poor, only 70% of algal cells flocculating at a dose of 1.0g/L, and that calcium hydroxide had significant damage to cells.Polyacrylamide had no flocculating effect on Monoraphidium sp.cells.