Papilio demoleus (Linn.) is a serious pest of lemon plants and some other host plants and worldwide distributed. It caused a great loss to citrus. Severe infestation of this pest almost 85% defoliation of citrus plants and retard the growth as well as decreased the yield of fruits caused great economic loss. The developmental stages, caterpillars are the voracious foliage feeder. For the biological and morphometric studies, the insect were reared in laboratory. The biological and morphometrical data were collected and statistically analyzed. The female butterfly mostly, laid their eggs singly but sometimes 4 to 6 eggs in groups on fresh leaves as well as on tender part of shoots. Majority of eggs found on the under surfaces of leaves. The average size of eggs was measured as 1.08±0.13 mm in diameter with an average incubation period of 3.29±0.38 days at optimum temperature and humidity. The five instars were recorded in caterpillar stages. The morphometric variations of different developmental stages of Papilio demoleus, L. have been recorded the lemon was the most preferred host plant. Average larval period of Ist, IInd, IIIrd, IVth and Vth instars were observes as 2.27±6.03, 2.37±0.01, 2.51±0.25, 3.09±0.08 and 3.3±0.12 days, respectively. Pupal period was 7 to 9 days. The life span of adult fly 4.68±0.72 and female fly was 5.98±1.38 days. Average life cycle of insect completed within 24.02 days at the level of optimum temperature. The biology and development are mainly depends on the climatic conditions of that particular area, location and plant species on which it is feeding.