Organophosphorus insecticides are widely used in industry, agriculture, horticulture, domestic, and for public health applications. The consumption of insecticides in the household has almost risen exponentially. Over this half century there has been a significant increase in developmental disorders observed in humans which are thought to have an association with the exposure to pesticides in home environment causing family stress. In addition, abamectin as biocide is recently used as an insecticide. Very little information is available with regard to the sub-lethal effects of abamectin; therefore, the purpose of this work is to compare the toxicity of abamectin as a biocide with malathion and dimethoate as organophosphorus insecticides using the earthworm (Lumbricus terrestirs) as a biomarker. The earthworm was exposed to the tested compound in artificial soil for 7 days. The LC50 of these insecticides was determined. The effects of two concentrations (LC50 & LC25) of these insecticides were studied on the activity of acetylcholinesterase (AChE), glutathione-S-transferase (GST), acid and alkaline phosphatases (AcP & AlP), and the levels of the two neurotransmitters; gamma amino butyric acid (GABA) and L-glutamic acid. The data showed that the LC50 of abamectin, dimethoate and malathion was 2.99, 13.7, and 39.69 mg/ kg, respectively. This means that abamectin was the most toxic, while malathion was the least toxic. Both LC50 & LC25 concentrations of dimethoate and malathion had significant inhibitory effect on the AChE activity, while abamectin had significant excitatory effects. AcP and AlP activities were significantly increased with the LC50 and LC25 of all the tested insecticides. GST induction activity was significant by the treatment of dimethoate and malathion, while there was significant decrease after treatment with LC50 of abamectin. But there was a non-significant difference with LC25 of abamectin. The lethal and sub-lethal concentrations of the tested insecticides caused a significant induction in GABA and L-glutamic acid concentrations. The data showed that abamectin has the highest effect on the concentration of GABA and L-glutamic acid while dimethoate had the lowest effect. From these results, it could be concluded that abamectin had toxic effect compared to the tested organophosphorus insecticides, also the earthworm can be considered a good sensitive biomarker to test the toxicity of different compounds.