This study investigated the fermentation kinetics and thermodynamics of ascorbic acid production from Brewery Spent Grain (BSG) using Aspergillus flavus and Aspergillus tamarii. Ascorbic acid fermentation of A. flavus and A. tamarii was performed at a temperature of 30 degrees C, agitation speed of 100 rpm and pH 5.0 at 96 h of fermentation. The thermodynamics, kinetics of the growth parameters and ascorbic acid production were studied using Monod, Contois and Teisser models. Teisser model gave the best fit as it obtained the highest maximum specific growth rate (mu(max)) and correlation coefficient of 0.184 h(-1) and 0.997, respectively, at 40 degrees C, pH 5.0 and 0.6 g of BSG. The result showed that Teisser model gave a better description of each growth parameter. Hence, the production of ascorbic acid by A. flavus and A. tamarii is growth-associated.