The synthetic insecticides that are frequently used in mosquito control programs have developed insecticide-resistant mosquitoes. Thus, this study is aimed to evaluate the efficacy of essential oils from the arial part of leaf of Plectranthus parciflorus against adult Culex quinquefasciatus. The aerial parts of P. parciflorus was screened for its phytochemical constituents and used for adulticidal assay with stock solution of 5 g of the extract into 100 ml of water. A stock solution of the oil was prepared using 15% tween-40 solution as the diluent. Four different concentrations (62.5, 125, 250 and 500 ul/ml) of the extract with four replicates each. Forty (40) adults each of Culex quinquefasciatus were separately exposed to each extract concentration for 10, 20, 30, 40 and 50 mins. Rate of knockdown and mortality was recorded after each stipulated time intervals. The results revealed that the efficacy of the extract exposed to the samples increased with increased concentrations and duration of exposure. The knockdown and mortality rate of P. parviflorus oil against the Cx. quinquefasciatus samples were 200 (100%) and 148 (74%) respectively. This study revealed the susceptibility of adults Cx. quinquefasciatus to the extract as evident by the 50min LC50, KD50 and KD95 values of 49.223 µL/mL, 6.726 µL/mL and 110.438 µL/mL respectively. Results obtained from this study suggest that the aerial parts of P. parviflorus is an effective constituent in the formation of pesticides or insecticidal of Cx. quinquefasciatus. Also, based on the exposure time, studies are yet to identify any eco-unfriendly attributes. Hence, it is a recommendable plant-based species with adulticidal potential against Culex quinquefasciatus.