A systematic survey for myxomycetes was carried out in 2011–2014 and 2017 at 106 localities in mountain tropical forests of Bidoup Nui Ba and Chu Yang Sin national parks (Dalat Plateau, southern Vietnam). In total, the survey yielded 652 records, of which 358 were field collections and 294 were collections obtained from 819 moist chamber cultures prepared with samples taken from the bark surface of living trees, ground and aerial litter and coarse woody debris. Determinations resulted in 105 taxa from 28 genera and 10 families. More than half (61) of all taxa were classified as rare. One collection of Badhamia could not be clearly assigned to any described species. Forty-two taxa were recorded for the first time for Vietnam and all were new for both national parks. The number of recorded taxa, increasing in a near-linear fashion with the number of field seasons, since sporulation activity of different species varies from year to year. Among the four natural vegetation types: middle mountain polydominant (A), mixed broadleaf-coniferous (B), middle mountain open pyrogenic coniferous (C), and high mountain cloud forest (D), completeness of the survey was highest for the first one. A pattern of decreasing diversity with increasing eleva-tion was found. In contrast, the specificity of myxomycete assemblages increased progressively in the sequence of vegetation types from A to D. In addition, artificial banana plantations (E) comprised the most distinctive but as well the least diverse myxomycete assemblage among all studied vegetation types. The taxonomic composition of myxomycete assemblages on major substrate groups differs from that in lowland forests, and species diversity increased from bark and aerial litter to ground litter and wood. © 2019 J. Cramer in Gebrüder Borntraeger Verlagsbuchhandlung, Stuttgart, Germany.