The following conclusions were obtained from the batch coagulation experiment for several coagulants such as alkaline water, PAC, Chitosan, and Ca(OH)₂ in order to compare the removal efficiency of microalgae by these coagulants. When alkaline water was used as a coagulant, removal efficiency of turbidity 95.5 %, DCW 95.4 %, OD 96.3 %, Chlorophyll-a 97.7 %, and PO4-P 76.1 % was obtained. When PAC was used, the effects of turbidity 98.2 %, DCW 99.5 %, OD 99.5 %, Chlorophyll-a 99.7 %, and PO₄-P 99.4 % were obtained. Turbidity 96.4 %, DCW 98.0 %, OD 97.6 %, Chlorophyll-a 97.6 %, and PO₄-P 20.8 % on by using Chitoson, and turbidity 89.4 %, DCW 95.8 %, OD 95.9 %, Chlorophyll-a 98.8 %, and PO4-P 87.3 % were able to be accomplished on Ca(OH)₂ coagulant. The amount of sludge produced by coagulation after 40 minutes of settling time with each coagulant, as alkaline water, PAC, chitosan and Ca(OH)₂ was shown to be 4.5 mL, 95 mL, 5 mL, and 10 mL. And the Chlorophyll-a concentrations in each flocculated sludge by different coagulant were measured as 48,800, 5,310, 35,750, 4,180 mg/m³, respectively. Alkaline water can be used as a coagulant without adjusting the pH, and the produced flocculation sludge is excellent in settling properties and can be used as a biomass of high compressed chlorophyll-a, so it is considered to be excellent as a eco-friendly coagulant.