Daqu, a complex starting material used for Baijiu production, contains microorganisms, enzymes, and volatile compounds. An important part of Daqu production is aging, but the physicochemical and microbial changes during aging remain largely unknown. This study characterized aging according to physicochemical parameters, volatile compounds, and microbial communities. Aging was found to aid in the stabilization of the physicochemical parameters. Solid-phase microextraction-gas chromatography-mass spectrometry was used to detect 72 types of volatile compounds, which were predominantly alcohols, esters, aldehydes, alkenes, and alkanes. During aging, these compounds changed considerably, but their structures eventually stabilized. A high-throughput sequencing approach was used to analyze the changing composition of the microbial communities. In general, aging helped to enrich and stabilize the microbial population for making Baijiu. A total of 35 bacteria were detected as prokaryotic; among these, 15 had a diversity abundance ratio of more than 1%. The dominant bacteria were from the genus Pantoea, but these decreased with aging, while bacteria from Lactobacillus and Weissella increased. After aging for 2 months, Pantoea, Lactobacillus and Weissella accounted for 0.4%, 54.0%, and 18.9%, respectively. A total of 12 eukaryotic yeast and fungi were detected, the most abundant of which were Incertae_Sedis_incertae_sedis, Saccharomycopsis, Trichocomaceae unclassified, Pichia, Tremellales_unclassified, and Galactomyces. During aging, the levels of Trichocomaceae_unclassified, Saccharomycopsis, and Galactomyces initially decreased but then increased. Pichia stayed unchanged as aging progressed. In conclusion, aging led to rebalanced interactions among Daqu microbes and was important in improving Daqu quality and ensuring its stability. (C) 2018, The Society for Biotechnology, Japan. All rights reserved.