Harvesting of marine Chlorella sp. by autoflocculation and flocculation by addition of coagulant with pH adjustment was investigated in this study. Autoflocculation provided low efficiency. Response surface methodology was employed to optimize the coagulant dosage and pH for flocculation. Aluminium sulfate and ferric chloride were investigated coagulants. The empirical models from RSM are in a good agreement with the experimental results. The optimum flocculation was achieved at ferric chloride dosage 143 mg/L, pH 8.1 and settling time 40 min. Biomass concentration also presented the significant effect on harvesting efficiency. Lipid extracted from marine Chlorella sp. cultivated in urea fertilizer medium with hexane as a solvent is suitable to produce biodiesel according to it contains high proportion of saturated fatty acids. The crude lipid should be purified to remove some impurities before making biodiesel. As the free fatty acid content was higher than 1% a two-step biodiesel production is recommended. (C) 2013 Elsevier Ltd. All rights reserved.