In this study, starches obtained from wheat, potato, and corn were used to synthesize cationic starches (CS), and the flocculation efficiency of these materials was tested with Chlorella pyrenoidosa and Botryococcus braunii cultures under different conditions. Our results indicated that these three CS had differing degrees of substitution following identical synthesis conditions. The various CS functioned similarly in this study, and the desired harmless flocculation efficiency was obtained at low dosages, with CS to microalgal biomass ratios of approximately 89 and 119 mg g(-1) for C. pyrenoidosa and B. braunii, respectively. Impressive harmless harvesting efficiencies were obtained at lower dosages with respect to appropriate stirring time before the settling, with ratios ranging from 58 to 78 mg g(-1) for C. pyrenoidosa cultures. The cost of microalgae harvesting can be cut dramatically by choosing cheaper starches prior to the synthetic CS and by applying suitable flocculation procedures.