Preliminary design calculation of a unit operation is always necessary to determine an order of magnitude of the proposed chemical plant. This paper describes an application of a spreadsheet in preliminary design of a bioreactor. There are a few steps in bioreactor design which are mass/mole balances and energy balances calculations before carrying out the bioreactor sizing. A spreadsheet was used as a tool to make a quick and accurate calculation. Glutamic acid fermentation is used to describe the overall method in this bioreactor design via spreadsheet. The method presented here is easy to learn and easy for the designer to scale up and to simulate different operating conditions to meet an optimum design from time to time by changing only a few variable Such as flow rate and substrate concentration of the feed in the previously constructed spreadsheet. (C) 2003 Elsevier Ltd. All rights reserved.