Glutathione (γ-glutamyl-cysteinylglycine) is a major thiol compound that plays various roles in vivo. This study focused on intracellular glutathione levels and on the influence of the environmental stresses on the levels under filter culture condition in Aspergillus oryzae. The profile of the levels showed a peak on the second day after inoculation. Under oxidative stress, the levels did not change. The levels increased under heavy metal stress and decreased under nitrogen source deficient condition.