In this study, the toxicity of ammonium was removed in the microalga Nannochloropsis oculata by using acetate as a carbon source. Algal biomass and lipid production were significantly enhanced when N. oculata was grew on 0.5-50 mM of ammonium and 16-64 mM of acetate in mixotrophic conditions. When grown mixotrophically on 1 mM of ammonium and 32 mM of acetate, the biomass and lipid production reached 543 mg/L and 279 mg/L respectively, which were 1.5 and 9.4 times higher than the levels generated when grown autotrophically on nitrate. This suggests that mixotrophic growth with acetate can be a useful method to enhance microalgal lipid production. (C) 2016 Elsevier Ltd. All rights reserved.