Olea europea L. emerged as a good source of traditional medicine for the treatment of various ailments of various countries of the world, in particular Mediterranean countries. In this study, oleuropein (1), oleanolic acid (2), maslinic acid (3), a mixture of erythrodiol and uvaol (4 and 5) isolated from the leaves of olive were added at two concentrations (1g/100g feed and 4g/100 g feed) into fish feed. Oreochromis niloticus (Nile tilapia) were fed twice a day with the feed during 96 hours. The levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) enzymes and glucose levels in the serums of fishes fed with pure compounds were found to be higher as compared with the control group. Pure metabolites affect the liver metabolism of Nile tilapia. These results suggested that the compounds tested affect the liver metabolism of Nile tilapia. Compounds 1, 2, 3 and 4+5 (2.5, 5.0 and 7.5 mg/Petri dish concentrations) were also tested for contact toxic effects against three important stored pests, Sitophilus granarius (weevil), Tribolium confusum (confused flour beetle) and Acanthoscelides obtectus (bean weevil). The toxic effects of the metabolites were lower than those of the insecticide, dichlorvos (DDVP). DDVP caused complete mortality of the insects after 48 hours of treatments, the metabolites caused the mortality rates T. confusum and A. obtectus, respectively. Maslinic acid (3) has the most toxic compound with the lowest LC 50 values (0.66 mg/Petri, 0.61 mg/Petri and 1.71 mg/Petri for S. granarius, T. confusum and A. obtectus, respectively). These results show that maslinic acid (3) as well as other substances can be used as natural insecticides against these pests.