Throscidae is a small family belonging to the polyphagan superfamily Elateroidea. Fossil throscids with a large morphological variety have been discovered from Cretaceous and Cenozoic amber deposits. However, only one of them has been reported from the fossil-rich Cretaceous Burmese amber so far. Here we describe and figure the second throscid beetle in mid-Cretaceous Burmese amber (ca. 99 Ma), Trixagosoma guangyuani gen. et sp. nov. The new fossil species has Trixagus-like short mesotarsal grooves and Potergosoma-like prosternum with nonparallel carinae. Our phylogenetic analysis indicates that it represents an early branching lineage of Throscidae. Its short mesotarsal grooves on metaventrite might represent an early evolutionary stage of this structure.