Abstract:[Background] The molecular mechanism of fruiting body development in mushroom-forming fungi, especially the transition from mycelium to primordium, is still unclear. Most of related studies focused on limited fungal species or environmental factors, and offered little information on the key genes in the development of mushroom-forming fungi. [Objective] This paper aims to study the molecular mechanism for primordium formation of mushroom-forming fungi. [Methods] RNA-seq data of 11 fungal species and 4 related environmental factors were analyzed. [Results] The number of up-regulated genes ranged from 325 (Pleurotus tuoliensis) to 2 854 (Rickenella mellea), while that of down-regulated genes was in the range of 379 (Pleurotus tuoliensis) to 3 189 (Armillaria ostoyae) compared with that of the control. As for the gene ontology (GO) terms, the top three biological processes were oxidation-reduction process, metabolic process and carbohydrate metabolic process. The mainly involved cellular components were the integral component of membrane, nucleus, and membrane, and the related molecular functions were hydrolase activity, oxidoreductase activity and catalytic activity. [Conclusion] There are some common key pathways for the primordium formation among mushroom-forming fungi.