Eight species of butterflies are recorded from among four different island groups in Yap Outer Islands, Federated States of Micronesia (FSM). Five species (63%) belong to the family Lycaenidae; the three others to Nymphalidae. Hypolimnas bolina is the most ubiquitous species, being the only one recorded on all the islands. Ngulu Atoll, which has the smallest land area, also has one of the most depauperate butterfly faunas, with only two species recorded, but it is located between Palau and Yap proper, which host the richest butterfly faunas in southwestern Micronesia. Ulithi Atoll, which is nearest to potential source populations on Yap, has the largest number of species. Small island size, limited habitat diversity, and lack of sufficient host plants combined with distance from potential source populations are likely to be the main factors contributing to the small number of species on these low-lying coralline islands.