Background. Lecanicillium lecanii is an entomopathogenic fungi, which was isolated from insect suffer from a disaster. Now, it is an effective bio-control resource that can control agricultural pests such as whitefly and aphids. There are many studies on the control of various agricultural pests by L. lecanii, but no report on its control of Bemisia tabaci biotype-Q exists. In this work we studied the susceptibility of B. tabaci Q-biotype (from Ningxia, China) to L. lecanii JMC-01 in terms of nymph mortality and the changes in detoxifying protective enzymes activities. Methods. Bemisia tabaci nymphs were exposed to L. lecanii JMC-01 conidia by immersion with the host culture. Mortality was assessed daily for all nymph stages. The detoxifying and protective enzyme activity changes, weight changes, and fat, and water contents of the nymphs were determined spectrophotometrically. Results. All instars of B. tabaci died after being infested with 1×108 conidia/mL. The 2nd-instar nymphs were the most susceptible, followed by the 3rd-instar nymphs. The corrected cumulative mortality of the 2nd- and 3rd-instar nymphs was 82.22% and 75.55%, respectively. The levels of detoxifying and protective enzymes initially increased and then decreased. The highest activities of carboxylesterase (CarE), acetylcholinesterase (AchE), peroxidase (POD), and catalase (CAT) occurred on the 3rd day, reaching 10.5 U/mg prot, 0.32 U/mg prot, 20 U/mg prot, and 6.3 U/mg prot, respectively. These levels were 2.2-fold, 4.3-fold, 2.4-fold, and 1.4-fold the control levels, respectively. The highest activities of glutathione-S transferase (GSTs) and superoxide dismutase (SOD) on the 2nd day were, respectively, 64 U/mg prot and 43.5 U/mg prot. These levels were, respectively, 2.7-fold and 1.1-fold that of the control level. The water and fat content in the infected B. tabaci nymphs decreased and differed significantly from the control levels. The weight increased continuously in the first 24 h, decreasing thereafter. At 72 h, the infestation level was about 0.78-fold that of the control level. Conclusions. The studied L. lecanii JMC-01 strain is pathogenic to the B. tabaci Q-biotype. This strain interferes with the normal functioning of detoxifying and protective enzymes, and is also involved in the disruption of normal physiological metabolism in B. tabaci.