Fed-batch culture of Aspergillus oryzae on maltose medium for glucoamylase production was investigated. The specific glucose consumption rate (delta) was used as an indicator of glucoamylase production and for feed rate control. During this fermentation, cell concentration was estimated continuously by the CO2 evolution rate which was, in turn, used to calculate the optimal feed rate. The statistical regression model was applied for the construction of a feeding strategy for a fed-batch culture. With this model, the feed rate was used as an operating variable while cell concentration and delta were used as the state variables. The optimal feeding profile for the glucoamylase production could be estimated from the predicted results. Glucoamylase production during the fed-batch culture employing delta as an indicator was 34% higher than that obtained by a constant feed rate.