Silkworm fed on mulgerry leaves with 1000 times diluted Insegar(main component : Fenoxycarb, ethyl-2-(4-phenoxyphenoxy)ethylcarbmate) and its effects was investigated on increase of the 5th larval silkgland weight and silk quality. The oral application of fenoxycarb showed increase of the silkgland weight. The whole period of the silkgland weight falls on the 2nd instar treatment by 13%, the 3rd day of the 4th instar by 111%(3100 mg) and the whole period of the 5th instar treatment rather decreased it by 66%(497 mg), as compared to 1470mg of the control. Female and male both increased 15%(1779mg) and 12%(1554mg) of the silkgland weight with the 2nd instar treatment, as compared to 1548mg and 1391mg in control, respectively. 118%(3368mg) and 104%(2832mg) of increase in the silkgland weight were also showed with the 3rd day of the 4th instar treatment but 70%(463mg) and 61%(539mg) of decrease were shown with the 5th instar treatment. The maximum weight of the middle silkgland weight increased by 6%(1248mg) and 127%(2673mg) with the 2nd instar and with the 3rd day of the 4th instar, respectively but 67%(393mg) of decrease took place, as compared to 1175mg of the control. The maximum increase of the posterior silkgland weight with whole peried of the 2nd instar treatment increased 12%(419mg) and 75%(656mg) and 64%(135mg) of decrease was shown, as compared to 374mg of the control. The oral application of Insegar at the 2nd instar increased 26 m of cocoon length, 4.0 cg of the cocoon filament weight and 0.21d of the silk denier, as compared to 1147 m of the cocoon length, 38 cg of the cocoon filament, 2.99d of the silk denier, weight of cocoon filament and silk denier, respectively but denier variance narrowed to 0.33d, as compared to that of the control.