Many plant species produce substances that protect them by killing or repelling the insects that feed on them hence effective natural insecticides could be extracted from such plants. Insects are the principal vectors of the pathogens causing many human, animal and plant diseases. The synthetic pesticides formulated for the control of these insect pests have been associated with some forms diseases in humans. There is need therefore to develop safe alternatives. Acanthus montanus is a plant who from observation seem to possess chemical compounds with insecticidal properties. This research evaluated the insecticidal potentials of ethanol extracts from the leaves of Acanthus montanus. Selected insects were exposed to ethanol extracts from the leaves and observed for 24 hours. Percentage mortality was calculated and compared with that of “SWAN” a synthetic insecticide. A GC-MS analysis of the plant extract was also carried out to determine the active constituents present in the extract. The result showed that the ethanol extract was substantially effective as an insecticidal agent as revealed by the mortality rates observed for insects treated with the plant extract as against those treated with the positive and negative controls. The GC-MS result of the extract showed a total of 22 peaks. Predominant among them were; 9, 12, 15 Octadecatrienoic acid (30.91%), followed by squalene (12.39%), and n hexadecanoic acid (11.68%). Other constituents were; Phytol (8.68%), Octadecanoic acid (7.06%) and 1-Octadecyne (5.62%). The plant has proven to be a potential source of organic pesticide which can be exploited in combating agricultural and domestic pests.