The genus Spirodecospora has been placed in Xylariaceae based on morphological similarities. Spirodecospora spp., found on bamboo in Japan, were taxonomically and phylogenetically studied using molecular data for first time. Molecular phylogenetic analyses were based on the DNA sequence data of three regions: the nuclear ribosomal internal transcribed spacer (ITS) region, the large subunit (LSU) of rDNA, and the second largest RNA polymerase II subunit (rpb2) gene. Results showed that Spirodecospora formed an independent lineage from other known families in Xylariales. The new family Spirodecosporaceae is introduced in this study to accommodate this lineage based on the phylogenetic evidence and morphological differences from the other known families. Spirodecospora is characterised by having deeply immersed ascomata with a cylindrical ostiolar neck, unitunicate, cylindrical asci with I+, wedge-shaped apical ring, and broadly ellipsoidal to fusoid, aseptate, brown, verruculose ascospores with spirally or almost straight linear ornamentation. Based on morphological observations and molecular phylogenetic analyses, S. melnikii and two new species of Spirodecospora, S. paramelnikii and S. paulospiralis, are described and illustrated. A key to the four accepted species of Spirodecospora is provided. Citation: Sugita R, Hirayama K, Shirouzu T, Tanaka K (2022). Spirodecosporaceae fam. nov. (Xylariales, Sordariomycetes) and two new species of Spirodecospora. Fungal Systematics and Evolution 10: 217-229. doi: 10.3114/fuse.2022.10.09.