The effect of an artificial diet on the developmental rate, a life history parameter, was examined for the swallowtail butterfly, Papilio xuthus. Artificial insect diets are an essential component of many insect rearing systems that produce insects for research purposes. Complex agar-gelled diets are generally prepared in large batches and used shortly after preparation because the degradation of perishable diet ingredients, such as vitamins and fatty acids, can adversely affect insect quality (Brewer F D 1984). However, the timing of diet preparation may be inconvenient and large batches wasteful if the unused, excess diet is discarded. This study showed that if the artificial diet was fed during the larval stage, the larval and pupal developmental periods, the percentage of pupation, and the pupal weight generally did not differ significantly among the five artificial diets evaluated. The percentage of pupation varied considerably, with no significant differences among diets except for diet C. A maximum pupation percentage of 83% was observed on diet C. Pellet-type diets were investigated with the aim of developing a more easily prepared diet. The extrusion of the artificial diet under high temperature and pressure may induce desirable chemical and physical changes in the extruded product. The purpose of the present study was to develop an artificial diet for rearing P. xuthus.