The larvicidal activity of Biostop Moustiques® (BM), a botanical biocide, was studied on susceptible and resistant strains of Anopheles gambiae s.s. at the concentrations of 1, 5, 10 and 20 mL/L of water. In addition to mortality and total protein concentration, the effect of BM on the activity of the following metabolic enzymes was evaluated in fourth instar larvae: glutathione-S-transferase (GST), alkaline phosphatase (ALP), superoxide dismutase (SOD), lactate dehydrogenase (LDH) and glucose 6-phosphate dehydrogenase (G6PDH). BM caused more than 90% mortality at different larval stages and had median lethal concentration (LC50) of 8.13 mL/L in susceptible Kisumu strain and 8.08 mL/L in resistant Acerkis strain. Protein concentration increased significantly in both strains when BM concentration was higher than 1 mL/L. GST and ALP activities increased significantly in both strains. LDH activity increased in Kisumu strain at 5 mL/L and decreased in Acerkis strain at all concentrations. G6PDH activity significantly increased with a maximum effect at 1 mL/L for Acerkis and 5 mL/L for Kisumu. BM completely suppressed SOD activity at 10 mL/L for Kisumu strain and 1 mL/L for Acerkis strain. This study showed that BM had a high larvicidal activity against both strains of Anopheles gambiae and it elicited a wide range of physiological changes.