A continuous thermophilic acid fermentation experiment was per formed using kitchen garbage to investigate relationship between microbial composition and products in acid fermentation processes Hydrogen fermentation occurred under the longer SRT condition, and when SRT was set at shorter lactate production increased, and butyl ate and hydrogen production decreased Simultaneously, microbial composition change from Clostridium spp to Bacillus spp. especially Bacillus coagulans was observed using random cloning method Clear relationship between B coagulans ratio and lactate concentration was obtained, but random cloning method is time and cost consuming. and not preciously quantitative Applicability of real-time PCR quantification to monitor change in B coagulans in kitchen garbage fermentation was verified Acid fermentation produces many kinds of organic acids such as lactate. butyl ate and acetate. and hydrogen gas, and similar operational conditions are proposed for hydrogen and lactate fermentations Real-time PCR quantification methods would be useful for developing a new monitoring tool for acid fermentation, especially with complex substrates, where many kinds of bacteria compete with each other in the same reactor (C) 2010 Elsevier Inc All rights reserved