Abstract: The characteristics of carboxylesterase, glutathione S transferase and acetylcholinesterase were investigated in Trialeurodes vaporariorum , fed on pumpkin, and Bemisia tabaci , fed on cotton. The comparative studies revealed that the resistance mechanisms of T. vaporariorum may be distinguished with that of B. tabaci in carboxylesterase(CarE), acetylcholinesterase (AChE) and glutathione S transferases(GSTs). The activity of CarE in B. tabaci strain was higher than that in T. vaporariorum while the comparision of Michaelis constants( K m) of CarE between B. tabaci and T. vaporariorum showed that the affinity of the former to substrate was much stronger than that of the latter. The activity of AChE mainly distributed in 23 mOD/(min· fly) in B. tabaci on cotton and 1015 mOD/(min·fly) in T. vaporariorum on pumpkin, respectively. The activity of AChE in B. tabaci on cotton was far lower than that in T. vaporariorum . The comparison of Michaelis constants ( K m) of AChE between T. vaporariorum and B. tabaci indicated that the affinity of B. tabaci on cotton to substrate was much weaker than that of T. vaporariorum strain. The activity of GSTs of B. tabaci was far higher than that of T. vaporariorum and the affinity of the former to substrate was stronger than that of the latter.