Insecticidal property of essential oils of lemon grass (Cymbopogoncitratus (Dc.ex.Nees)), cinnamon (Cinnamomum bejolghota (Buch.-Ham.) Sweet) and clove (Syzygium aromaticum (Linn.))against adult of mealybug (Pseudococcus jackbeardsleyiGimpel&Miller) was evaluated by using direct spray method.As for the bioassay, 5% essential oils were applied for 5 ml by Potters spray tower under 10 lbf/sq in.The mortalities of mealybug were observed at 24 hrs after treatment.The result showed that essential oil of lemon grass in corporate with petroleum oil, Tween-20 and white oil was the most toxic to the mealybug, they all caused 100% mortality.The essential oils of clove and cinnamon in corporate with petroleum oil could kill mealybug with more number than that in corporate with Tween-20 and white oil with non-significant difference at P<0.05.Contact effect of thoseessential oilsat variousconcentrations of 0, 1, 2, 3, 4 and 5% in corporate with petroleum oil against mealybug was thenevaluated.Based up on 24 hrsLC50 values, the essential oils of lemon grass was the most toxicto the insect whichpresented 1.82%,followed by the essential oils of cinnamon and cloveshowed2.40and 3.09%,respectively.