Diderma microsporum is a taxonomically controversial species of Myxomycetes. Currently, it is treated as a synonym for Diderma effusum. In this study, two specimens from Lafa Mountain National Forest Park in Jilin Province of China were researched concerning morphology with the light microscope and scanning electronic microscope and compared with the holotype from Japan to confirm that the species was first discovered in China. It is mainly characterized by cushion-shaped plasmodiocarps; single peridium, ornamented with dense flake-like lime crystals on the outer surface; columella absent; capillitium (0.99–)1.29–2.05(–2.30) μm diam, with spindle-shaped enlargement forms at branching points, decorated with dense small warts; spores (5.70–)6.49–6.87(–7.61) μm diam, warted and with clusters of large warts. In addition, the partial nucleotide sequences of nuclear 18S rDNA and elongation factor-1 alpha genes of D. microsporum differed clearly from those of other Diderma species. The results supported the rationality that D. microsporum is an independent species. Light microscopic photos, scanning electron microscopic photos, and an emended description of morphological characters are provided.