1. The mode of action and some chemical properties of unknown growth factor required by the larvae of the smaller tea tortrix (Ado-xophyes orana FISCH. v. Rösl.) were elucidated by feeding response tests of newly hatched larvae and rearing experiments of the larvae on synthetic diets containing various fractions of tea leaves. The activities of unknown factor of some crude substances and pure compounds were also evaluated by rearing experiments.2. The rate of larval growth was positively correlated with the dietary amount of the waetr extract of tea leaves, the optimum range of the extract was considered to be 15-18% of dry diet. But percentages of larvae established on the food media were not correlated with the amount of the extract. It was concluded that the unknown growth factor contained in tea leaf was a nutrient essential for larval growth, but had no activity as a phagostimulant.3. The unknown dietary factor is neutral organic substance which is insoluble in benzene, chloroform, acetone, ethyl alcohol, ethyl acetate saturated with water, but soluble in hot water and 50-67% acetone, precipitated with neutral lead, and not absorbed to charcoal. And it was assumed that the factor consisted of at least two components.4. Other than tea leaf powder, strong growth factor activities were found in alfalfa concentrate, and water extract of yeast, and weak activities in granular yeast for bred, powdered yeast (Ebios), and rendered extract of meat. But not at all in rice plant concentrate, pepton, casein soda, bactocasitone, egg albumine, crude catechins from tea leaf, dextrin, and. soluble starch.5. Some pure compounds tested with negative results were as follows : Ascorbic acid, ten kinds of B vitamins contained in basal diets, vitamin B12, ribonucleic acid, glycine, cystine, glutamine, asparagine, arabinose, xylose, fructose, galactose, mannose, sorbose, rhamnose, sucrose, lactose, raffinose, trehalose, melibiose, cellulose, adonitol, mannitol, aconitic acid, citric acid, fumaric acid, maleic acid, malic acid, oxalic acid, succinic acid, and tartaric acid.6. These results obtained were compared to those of Pyrausta nubilalis and of Chilo suppressalis, and the characteristics and properties of these unknown growth factors were discussed.