Ants and ant-aphid associations in the Mariana Islands of Guam, Rota, Tinian and Saipan are reported from collections made by the authors from 1997 to the present. Earlier collectors’ records are also presented. With one possible exception, all ants collected in the Marianas Islands were exotic, invasive species originating from the neo-tropics, Australia, Africa or Asia. Similarly, all aphids collected from these islands were exotic invasive species, four of which have become serious crop pests. Six major neo-tropical ant species in the subfamilies Formicinae, Dolichoderinae, and Myrmicinae were frequently associated with the four economically important aphids Aphis gossypii, Aphis craccivora, Toxoptera citricida and Pentalonia nigronervosa. Five minor ant species in the subfamilies Myrmicinae and Formicinae originating from Africa or Asia were also collected. At least seventeen collected ant species were not associated with aphids. Surveillance surveys at airports, seaports, warehouses and tourist areas suggest that red imported fire ant, Solenopsis invicta, the little fire ant, Wasmannia auropunctata, and the Argentine ant, Linepithema humile, are not yet present in the southern Mariana Islands. However, workers of Lepisiota sp. have been collected near stored cargo containers at the Guam airport, constituting a new island record of this genus for Guam.