Juvenile hormone is the most important hormone inside the insect, but its circulating titer should be under tight control. Then enzymes involved in JH metabolism, especially juvenile hormone esterases (JHEs) play critical roles in insect metamorphosis and reproduction. Within a set of 11 JHEs predicted in the diamondback moth (DBM) genome, Plutlla xylostella (Linn.) we identified one gene that contained the main functional motifs of insect JHEs. Its expression and transcript levels during egg, different instar of larvae, prepuae, pupae and adult stages were measured. Also, its expression in the epidermis, midgut and fatbody of the 4 th instar larvae was compared. The changes in enzyme activity in the 4th instar larvae were determined.