The comparative studies under laboratory conditions have been carried out to investigate the influence of different alternative host plants viz., bael [Aegle marmelos (L.)], curry leaves [Murraya koenigii (L.) Spreng.], ber (Zizyphus mauritiana Lam.) and lemon [Citrus limon (L.) Burm.f.] on biology and morphometrics of Lemon butterfly, Papilio demoleus (Linn.). The lemon is the most preferred host of P. demoleus used as a controlled experimental host plant. The variations in periods of larval, pupal and rate of emergence into adult have been recorded and found that the lemon was the most preferred host plant on which all the larval stages survived smoothly. The caterpillars when reared on alternative hosts showed an increase in average larval period. The average survival percent of larvae were reported highest on bael leaves, followed by curry leaves and ber leaves. Similar patterns of results were also recorded on the pupal period and rate of emergence with alternative hosts. The morphometric variations in weight, size and colour of caterpillars, pupae and adults were also measured and found in decreasing order of host preferences as lemon[greater than]bael[greater than]curry[greater than]ber.