A neutralizing agent is usually employed to counteract the pH reduction during lactic acid fermentation by Rhizopus oryzae. Calcium carbonate (CaCO 3 ) is used as such a pH controlling agent. The low solubility of CaCO 3 in the fermentation broth could however lead to low efficiency in pH control and cause problems in the subsequent purification process. Therefore, an alternative agent in place of CaCO 3 was examined in this study. The effect of four different neutralizing agents, including CaCO 3 , sodium hydroxide (NaOH), ammoniacal solution and sodium bicarbonate (NaHCO 3 ) on lactic acid production and the morphology of the pellets were investigated. Results indicated that CaCO 3 was still the preferred choice, because of the pellet morphology and the highest lactic acid concentration (43.3 g/L) obtained in the batch using 60 g/L of sweet potato starch as feedstock. It is noteworthy that the lactic acid purification is relatively easier when using NaHCO 3 instead of CaCO 3 , due to the higher solubility of sodium lactate than calcium lactate. Therefore, even the batch with CaCO 3 had a slightly higher productivity (1.23 g/L/h) than the batch with NaHCO 3 (1.14 g/L/h), NaHCO 3 might be the first choice for process designers whenever recovery is vital.