Sexual selection via mate choice has been implicated in the evolution of sexual dimorphism and female polymorphism. Although mate choice based on wing colouration has been documented in butterflies, empirical evidence remains scant and is limited to a handful of species. Furthermore, male and female mate choice have rarely been studied in the same species, although both are known to occur in butterflies. In this study, behavioural experiments were conducted to investigate female and male mate choice in the Common Mormon Papilio polytes, a swallowtail butterfly which exhibits female-limited mimetic polymorphism. By artificially reducing male dorsal brightness, we found that mimetic and non-mimetic females did not prefer to mate with brighter males, whereas male size seemed to influence female mate choice. As there was a positive correlation between male size and brightness, female preference for larger males might lead to the evolution of sexual dimorphism in dorsal brightness. In the second part of this study, we offered male butterflies a choice of mimetic and non-mimetic females, and found that males mated preferentially with the mimetic female form. The hypothesis that male mate choice is involved in the persistence of the non-mimetic female form was therefore not supported. Future studies could investigate the role of female mate choice in the evolution of female-limited mimicry, as well as potential factors (e.g. female pheromones) that affect male mate choice.