Since there are only limited biogeographic studies of myxomycetes in Southeast Asia, this study was conducted to assess the molecular diversity of Diderma hemisphaericum, a cosmopolitan myxomycetes species that abundantly occurs in most moist chamber collections in tropical Southeast Asia. Specimens that contain D. hemisphaericum were gathered from various parts of the Philippines: (i) Los Banos, (ii) Calauan, (iii) Basud, (iv) Isarog and (v) Malilipot; and Vietnam: (i) Thai Nguyen (ii) Ha Noi and (iii) Da Nang. Using modern molecular techniques, the common barcode nuclear marker 18S rDNA for myxomycetes was targeted for the 50 specimen used in this study. A total of 27 ribotypes (11 from the Philippines and 16 from Vietnam) were obtained. The Mantel test showed that genetic differentiation among ribotypes is not correlated with geographic distances. The FST index (0.083) indicates high genetic intermixing between the Philippines and Vietnam. Hence, it seems that the variation across regional scale gene pool is not directly influenced by geographic isolation but rather by environmental selection.