The aim of this study was to determine the optimal conditions for adding eggshells as a bioflocculant (including concentration dosage, pH, mixing time, mixing rate and settling time) in harvesting Chlorella vulgaris cells from liquid cultures, using the well-known jar-test experimental method. Eggshells separated successfully 99 § 0.4% of the C. vulgaris biomass at the following optimal parameters: eggshell concentration 80 mg/L, mixing time 20 min, mixing rate 150 r/min and settling time 20 min at pH 6. These results indicated that eggshells, as a biopolymer, are a promising flocculant due to their high separation efficiency, low dose requirements and short mixing and settling time. Eggshells not only act as an adsorbent, but also spontaneously coagulate to agglomerate the microalgae cells.