ABSTRACT Papilionidae, swallow-tailed butterflies, attract the attention of biologists for the importance of their ecological and evolutionary study. Papilionidae are peculiar among Lepidoptera for their larvae bearing a Y-shaped eversible osmeterium on the prothorax. However, morphological study of the larvae of Papilionidae, especially in terms of the osmeteria, are far from satisfactory. In this study, larval ultramorphology of Sericinus montela was described using scanning electron microscopy after a novel method of sample preservation. Larvae of S. montela are peculiar for the 15 teeth on the incisor, the triordinal mesoseries plus biordinal lateroseries of crochets on the anal prolegs, the urticating acanthae on secondary setae, and the micro openings and surrounding microtrichia on the osmeterium. The method of sample preservation, larval morphological characters and correlated defensive strategies are compared and briefly discussed.