The phenoloxidase (PO) is present as two types of isozymes (POI and POII) in the hemolymph of the last larvae of Spodoptera litura. Two isozymes have been separated through gel permeation chromatography and enzymatic characteristics of both POs investigated. It was confirmed that there is no effect of salt concentration on the activity of POs. In contrast, the addition of pigments from hemolymph to the test mixture revealed the increase of the activity of POII, but not POI. In the experiment to confirm the effect of organic compounds on POs activities, the activity of POI was significantly increased in the presence of 1-, 2-propanol, 50% ethylacetate, 50% DMSF or 5M urea. However, the activity of POII was increased only in the presence of acetone. From the present results, we concluded there are more than two types of inactive phenoloxidases, which are activated by non-self molecules, alcohols or organic compounds.