Insecticidal properties of essential oils of leaf and bark of Ceylon Cinnamonium zeylanicum Blume (Lauraceae), Cymbopogon nardus Rendle (Gramineae) and Cymbopogon citratus DC. (Gramineae) and their 10 compounds were investigated against Musca domestica (housefly). Cinnamomum zeylanicum bark and Cymbopogon citratus oils showed good knock down and mortality against M. domestica (LD50 1.37 and 1.71 mu g/insect, respectively) than C. zeylanicum leaf (LD50 2.75 mu g/insect) and C. nardus (LD50 3.10 mu g/insect) oils. Cinnamaldehyde (65%) was a major constituent of C. zeylanicum bark oil, eugenol (77%) in the C. zeylanicum leaf oil, geraniol (24.8%) in the oil of C. nardus and citral (78.8%) in C. citratus leaf oil. Cinnamaldehyde, eugenol, eugenyl acetate, geraniol and geranyl acetate were more active against M. domestica than their corresponding essential oils, while cinnamyl acetate, citral, citronellal, citronellol and alpha-terpineol were less active.