Fossil leiodids are sparse, and they are confined to the Cenozoic. Here we describe and illustrate the first definitive Mesozoic leiodid, Colonellus burmiticus sp. nov., based on two well-preserved adults from the Upper Cretaceous Burmese amber. The fossil is firmly placed in the extant Coloninae based on multiple synapomorphies, such as antennae with normal-sized antennomere 8 and abdominal intersegmental membranes with "brick-wall" pattern. It can be further assigned to the extant genus Colonellus (subgenus Pentacolonellus) by its five-segmented antennal club. The discovery suggests that Colonellus is an ancient group, originating no later than the mid-Cretaceous. (C) 2017 Elsevier Ltd. All rights reserved.