Many useful chemicals are produced through biological process. One of those chemicals is gluconic acid which has many industrial and daily uses. This acid is used in the pharmaceutical, food, animal feed, and textile industries. In addition, it is also added in cement production to control the setting time and increase strength and water resistance, and used as raw material for photographic developer. In metallurgy it is utilized for alkaline derusting. Production of organic acid such as gluconic acid by fermentation is preferable because of its low cost, mild process condition and possibilities to utilize renewable resources as the substrate of fermentation. The microorganisms which are usually exploited to produce gluconic acid are mold Aspergillus niger and Gluconobacter oxydans bacteria. The aim of this study is to investigate the dynamic behavior of gluconic acid production by Aspergillus niger in single continuous fermenter. The dynamic study will enhance understanding of the fermentation process and especially it will be useful in designing control strategy, selecting controller settings and optimizing process operating conditions. Instead of Logistic kinetic, the Contois kinetic parameters which had been studied previously were chosen, as it provides dynamic relationship among substrate, cells and product. The data was collected from batch fermentation experiment with initial substrate concentration of 150 g/l. and the kinetic parameters were determined using non linear least square curve fitting. Contois equation is used for cell growth, Luedeking-Piret equation for gluconic acid formation, and Luedeking-Piret-like equation for glucose consumption. The hydraulic retention time ( ) used was determined 24 h, while steady state conditions were obtained from steady state simulation. Here, we present the dynamic behavior of continuous fermentation for gluconic acid production under possible disturbances that might occur. Those three differential equations must be solved simultaneously to obtain cell, substrate and product profile. 24 hr cell, substrate and product concentration profile subject to step disturbance change of inlet substrate concentration with magnitude of -20 g/l (sudden change from 150 g/l to 130 g/l) at t = 10 hr. It can be seen that the outlet cell, substrate and product concentration exhibit approximately first order response to the substrate change. .