The effects of isopropyl-beta-D-thiogalactopyranoside (IPTG) induction conditions and cell growth sate on the production and excretion of Aeromonas hydrophila chitinase by Escherichia coli were investigated. The most efficient induction condition for chitinase production was obtained by adding IPTG at a final concentration of 0.5 mM to the medium at the fermentation time of 2 h. Specific chitinase production increased with decreasing cell growth rate, which was manipulated by decreasing the aeration level or NH4Cl concentration. Overexpression of the chitinase gene as well as the decrease in specific cell growth rate resulted in a high percentage of periplasmic enzyme excretion, Comparing the extracellular fractions of alkaline phosphatase (a periplasmic enzyme) to malate dehydrogenase (a cytoplasmic enzyme), the increase in outer membrane permeability is primarily attributed to chitinase excretion.