The yellow fever mosquito, Aedes aegypti (L.), is considered the primary vector for both dengue and yellow fever. Using insecticide is one of the major ways to control this medically important insect pest. However, few new insecticides have been developed for mosquito control. As part of our collaborative effort to search for new insecticides to control mosquito, piperidine was used as lead compound for further optimization. Herein, we report the toxicities of ten 1-undec-10-enoyl-piperidines against female adults of Aedes aegypti (L.). On the basis of 24-h LD50 values after topical application, the most toxic compound was 2-ethyl-1-undec-10-enoyl-piperidine (LD50=0.80 ƒÝg per mosquito). Piperine [(E, E)-1-piperoyl-piperidine], a commercially available insecticide ingredient, was less toxic (LD50=8.13 ƒÝg per mosquito) than all the tested ethyl- or methyl- derivatives of 1-undec-10-enoyl-piperidines. The toxicities of 1-undec-10-enoyl-piperidines were significantly decreased when a benzyl moiety was added to the carbon of the piperidine ring, regardless the carbon position to which it was conjugated. Taking together, these preliminary results could be a useful guide for further modification of the piperidine ring in the development of a potential insecticide.