A new species of the ‘flat-backed’ millipede family Polydesmidae, Propolydesmus cretaceus sp. nov., is described from the mid-Cretaceous Burmese amber. Detailed morphological characters are provided on the basis of 3 well-preserved adults (2 males and 1 females), 2 female subadults, and 14 additional specimens, using confocal laser scanning microscopy (CLSM) placed in the extant genus Propolydesmus. It majorly differs from other congeners due to the stronger gonopod acropodite and the presence of a bipartite gonopod exomerite.