Abstract: Chlorella sp. XQ-200419 is a lipid-rich strain with potential application in microalgal biodiesel. To study the effects of pH on the growth rate, areal biomass productivity, total lipid content, and areal lipid productivity of Chlorella sp. XQ-200419, the batch culture was conducted for 8 days with modified BG-11 medium in a pH range of 5.06.0, 7.08.0, 8.09.0, 9.010.0, 10.011.0, which was monitored by a on-line pH controller in a selfdesigned photo bioreactor that mimics the open circular pond. We observed that pH significantly regulated the photosynthesis, growth rate, areal biomass productivity, total lipid content and areal lipid productivity of Chlorella sp. XQ-200419 the pH range of 7.09.0 was the best condition for culturing Chlorella sp. XQ-200419 and no significant difference was existed in the pH from 7.0 to 9.0. Both pH values below 7.0 and above 9.0 significantly reduced the photosynthesis, growth rate, areal biomass productivity, total lipid content and areal lipid productivity compared with pH range of 7.09.0. The photosynthesis was consistent with the growth and lipid production of Chlorella sp. XQ-200419 at all pH conditions. Chlorella sp. XQ-200419 achieved the peak average areal biomass productivity 8.9 g/(m2d) and the maximal average areal lipid productivity 2269.5 mg/(m2d) in pH 7.08.0. The average areal biomass productivity and average areal lipid productivity decreased by 42.1% and 60% at the pH range of 10.011.0, respectively. Both the growth and lipid production were enhanced under suitable pH range, indicating that the effects of pH on the lipid production of Chlorella sp. XQ-200419 was a kind of fitting mode not stress mode. The current study not only evaluated the effects of pH on the photosynthesis, growth and lipid production of Chlorella sp. XQ-200419, but also provided a basis for controlling of proper pH in mass culture of Chlorella for algal lipid production.