It has been demonstrated that the treatment of juvenile hormone antagonist KK-42 can significantly accelerate growth of which has been applied in aquaculture, but the mechanism of KK-42 is unclear. To provide the theory support involved in KK-42 application, the temporal and spatial expressions of farnesoic acidMF) which is the important hormone regulating directly crustacean growth, was assayed and the effect of KK-42 on the enzyme was researched. ), 3.5−5.0 cm long, were randomly divided into two groups, soaked in KK-42 solution at a concentration of 1.95×10^-4 mol/L or in the solution without KK-42 for 1 min, respectively, and then cultured in normal way. The levels of FAMeT mRNA were determined using real-time PCR and hemolymph MF titer was analyzed by normal phase high-performance liquid chromatography. Results showed that the expression pattern of FAMeT derived from the muscle, eyestalk and mandibular organ (MO) tissues varied in control, of which, the mRNA levels in muscle and eyestalk tissues were not only relatively low but also little various during the experiment. However, an obvious fluctuation of mRNA level occurred in MO during the stage of experiment, more than 1-fold of increase in mRNA level was observed on days 2, 6, 7, and 8 comparing to that on day 0. The hemolymph MF content in control shrimps rose during the experiment. Administration of KK-42 resulted in the universal depression on FAMeT expression in three tissues mentioned above; the most significant inhibitory effect occurred in MO where the level of FAMeT mRNA was considerably lower than that in control group from day 1 to day 7; )) and 55.7% () on day1, day 4 and day 6 after KK-42 treatment, respectively. Meanwhile, the amount of hemolymph MF fell in KK-42-treated shrimps compared to that in control ones during the duration of the experiment, which might be involved in transcription depression in the animal tissues, especially in the MO. Our present study demonstrates that KK-42 can significantly inhibit FAMeT expression in the MO and muscle as well as eyestalk tissues of the shrimp and decrease the hemolymph MF titer, which may be one of the growth–promoting mechanisms of KK-42 on.