Haemolymph juvenile hormone(JH) titers were examined using Galleria cuticle wax test and gas liquid chromatography(GLC) and juvenile homone specific esterase(JHE) activities, which control JH, measured in both sexes of the gypsy moth, Lymantria dispar, during different larval stages, days and time. Galleria cuticle wax test had the highest JH titer at the 4th instar larvae on both sex(30,000 GU/g(♂), 33.000 GU/g( ♀)), and the lowest JH titer at the 5th instar larvae in male(17,000 GU/g), 6th instar larvae in female(6,000 GU/g). When JH titer was measured from day-1 to day-7 at the 4th instar larvae, it was high at day-2 in male(42,000 GU/g) and day-1 in female(37,000 GU/g), When JH titer was measured according to time, its high level was observed at 12 hour on both sexes(55,000 GU/g(♂) and 48,000(♀)). We found five JHs and three of them were identified as JH I, II, III, but two of them unidentified. 4th instar larvae showed a dramatic change of JH titers and female was me-re extreme than male. JH IIshowed the greatest change of its level regardless of different stages of larvae and sexes. JH I showed 0.029ng/m1( ♂ ), 0.015ng/ml(♀) at 4th instar larvae and specially JH III 0.0238 ng/ml at male 4th instar larvae, which is lower titer. Juvenile hormone specific esterase(JHE) activities of the gypsy moth in the different larval stages were lower at the 2nd instar larvae in male(0.8 mole/min/ml), and highest at the 5th instar larvae(3.6n mole/min/ml). When hydrolysis rate of JH at the 4th instar larvae whose JH titer was highest was measured, in male larvae, it was lowest(0.9n mole/min/ml) at day-5 and highest at day 7, and in female larvae, it was lowest(0.9m mole/min/ml) at day-1 and highest(3.3n mole/ min/ml) at day-4. Hydrolysis rate of JH in day-2(♂) and day-1 at the 4th instar larvae, whose JH titer was highest, was high in JHE activity at 6 hour(2.3 mole/min/ml) in male and 24 hour(4.7n mole/min/ml) in female. In conclusion, JH titer and JHE activity was shown to be inversely proportional.