The Java-Sumatra upwelling is one of the most important upwelling systems in the Indian Ocean, with maximum upwelling intensity in July through August. To estimate the nitrate supplied by upwelling, we developed a three-dimensional hydrodynamic model to calculate the mean vertical speed and determine the depth of upwelling. We used in-situ vertical nitrate profi les to assess nitrate concentration in the upwelled waters, and calculated the nitrate supply as the product of nitrate concentration and vertical transport obtained from the numerical model. The calculated result represents potential new production generated in the upwelling region. We found that on the event time scale (monthly) of Java-Sumatra upwelling, water brought to the surface originated from locations 100-m deep, giving a nitrate supply of 93.77×10 3 mol/s and potential new production of 1.02×10 14 gC/a.