Microbial flocculants for harvesting mass cultured Chlorella vulgaris were screened and that from Paenibacillus sp. AM49 was identified as the best. The flocculation efficiency of this bioflocculant increased with the pH within a range of pH 5-11 and was 83%, which was higher than the 72% and 78% produced by aluminum sulfate and polyacrylamide, respectively. The highest flocculation efficiency was with 6.8 mm CaCl2 as co-flocculant. The bioflocculant from Paenibacillus sp. AM49 can be used effectively to harvest C. vulgaris from large-scale cultures.