Abstract Background The investigation aimed to show the effect of two concentrations of (Protecto 9.4%) commercial formulation of Bacillus thuringiensis kurstaki (Bt) on some biochemical changes of the land snail Monacha cartusiana at three different experimental periods (24, 48 and 72 h). Also, some histobiological altrations of the snail at a lethal experimental period of 96 h were studied. Results Pathogenicity effect of two sub-lethal concentrations of biopesticide Protecto; LC20 (6.72 × 106 IU/mg) and LC40 (17.28 × 106 IU/mg) were studied on the land snail M. cartusiana at 3 different exposure periods (24, 48, and 72 h). Some biochemical parameters such as Alkaline phosphatase (ALP), Alanine amino transaminase (ALT), Aspartate amino transaminase (AST), and Total protein (TP) were investigated. These observations cleared that; a significant elevation of ALP, ALT, and AST increased with increasing the sub-lethal concentration of protecto (LC20 and LC40) against the exposed snail. Also, the activity of enzymes significantly increased with increasing the time of exposure (24, 48, and 72 h), respectively. Conversely, the level of TP in the snail was significantly decreased under pathogenic exposure for both (LC20 and LC40) concentrations of Protecto at the same three treated periods (24, 48 and 72 h). The histbiological examinations at LC20 and LC40 for the exposure period 96 h, showed that the digestive gland with vacuolated degenerated, ruptured digestive cells and hemocyte infiltration. Moreover, the foot was observed with necrotic changes, vacuolated connective tissue, as well as, deformation in muscle fiber, and rupture the outer layer. Conclusions Final results showed that protecto B. thuringiensis had a pathogenic effect on land snail enzymatic activities and histbiological structures of land snail.