Despite the development of insect resistance, water contamination and human health hazards, the farmers still depend on excessive application of synthetic chemical insecticides in agricultural practices. Plant-based extracts have been used as bio-pesticides in a wide range due to their toxicity and biodegradability, they complete and enhance the effect of traditional insecticides. They have a wide variety of bioactive secondary metabolite such as flavonoids, a class of polyphenols that have been studied for their role in mechanism of plant defense and their effect as insecticides for crop protection. Phytophagous insects are considered the most destructive pests on crops. The Brassica napus L., plant, known as rapeseed or canola, has defensive property against pathogens and phytophagous insects in field. Leaves of B. napus are considered as agro-waste, five flavonoids such as Kaempferol, Quercetin-7-O-glucoside, Kaempferol-3-O-glucoside and Quercetin., were isolated and identified from ethanolic B. napus leaves extract. This research evaluates insecticidal activity of B. napus flavonids, emamectin benzoate and combination of their sub-lethal concentrations on Spodoptara littorals and their effect on enzymes activities.  All combinations of sub-lethal concentrations of B. napus flavonoids and emamectin benzoate increased the mortality percentages of treated larvae, especially, LC₂₅ (0.664 g/100ml) of B. napus flavonoids with LC₁₀ (0.007 mg/L) and with LC₂₅ (0.012 mg/L) of emamectin benzoate. The mortality percentages increased by 95.22 and 78.66 Co-toxicity factor, respectively for two combinations. All treatments caused inhibition of phenoloxidase, α-esterase and β- esterases enzymes activities. The greatest inhibition of these enzymes occurred in mixture of LC₂₅ of B. napus flavonoids with LC₁₀ of emamectin benzoate. Phenoloxidase, α-esterase and β- esterases decreased by 60.75, 61.49 and 42.31%, respectively compared with un-treated larvae. The combination of LC₂₅ of B. napus flavonoids with LC₂₅ of emamectin benzoate caused 56.62, 49.50 and 32.11% inhibition in the enzymes activity, respectively. It was concluded that application of B. napus flavonoids enhance emamectin benzoate toxicity against S. littoralis larvae with less hazard effects on human health, environment and without development of insect resistance