The larvicidal activity of four commercially available essential oils  were tested on the  4th larval instar of Culex quinquefasciatus in the laboratory. These were the essential oils of Cinnamomum osmophloeum (cinnamon), Matricharia chamomella (chamomell),Nigella sativa(nigela) and Sesamum indicum (sesame) oils.  The toxicity index, LC50 values, LC50 values were 26, 32, 82 and 26 ppm for cinnamon, chamomell, nigela and sesame oils, respectively after 48 hrs from treatment. All tested oils, at high concentrations, had high larvicidal toxicity. Furthermore, the increase of concentrations was directly proportional to reduction in pupation rates and adult emergence. Significant decrease in pupation rate was observed by cinnamon oil at 65 ppm. Adult emergence was 100% inhibited in cinnamon oil was used, especially at concentrations 50 and 6were5 ppm. The number of eggs/ female  and eggs hatchability were also decreased by the application of all concentration of the tested oils. In addition, the tested plant oils exhibited various morphological abnormalities on larvae, pupae and adult stages The result from this study demonstrated that essential oil of cinnamon was the most potent oil and was the major cause of malformation of both larval and pupal stages.