Changes in haemolymph juvenile hormone esterases activity were examined the last instar larvae of Bombyx mori. Two major peaks of juvenile hormone specific esterase (JHE) were observed. The first peak occurred at 4-6 day and the second at the prepupa. The heights of the two peaks of JHE activity was not significantly different. The $alpha$-naphthyl acetate esterase ($alpha$-NAE) activity of both sexes increase at 4 day and exhibiting its maximum at 2 day of the spinning. A similar patterns of JHE and $alpha$-NAE activity were observed during the early last instar larae, however, a marked different were observed at 2 day of the spinning when $alpha$-NAE activity was highest and JHE activity was lowest. These results suggest that JHE plays an important role in regulation of JH titer during the last instar larvae of Bombyx mori comparing $alpha$-naphthyl acetate esterase.