Micromalthidae is a small relictual family of archostematan beetles that is well known for its unusual asexual reproductive system characterised by parthenogenetic, viviparous, larviform females and sterile adults. Here we describe the first micromalthid beetle from mid-Cretaceous Burmese amber (ca.100Ma). Protomalthus burmaticus gen. et sp. nov. differs from all presently known micromalthid beetles by the presence of distinct frontoclypeal, labroclypeal, and medicranial sutures. The finding represents the first Mesozoic record of an adult micromalthid beetle and confirms a Gondwanan distribution of the family during the Cretaceous. A list of micromalthid beetles is provided, together with a key to extant and fossil species.