Alkaline mixed culture fermentation (MCF) is a promising technology for reducing organic waste and producing biochemicals. However, chemostat metabolite spectra that are necessary for constructing a model and analyzing factors are seldom reported. In the present study, the effects of pH on the metabolites distribution in mesophilic (35 degrees C), thermophilic (55 degrees C), and extreme-thermophilic (70 degrees C) alkaline MCF were demonstrated. A chemical oxygen demand balance above 80% was achieved, and the main metabolites included acetate, ethanol, propionate, lactate, and formate. The yields of ethanol and formate increased as pH was increased from 7.5 to higher pH under mesophilic and thermophilic conditions, while the yields of acetate, lactate, and/or propionate decreased. The yields of ethanol, acetate, and formate increased under extreme-thermophilic conditions as pH was increased from 7.5 to 9.0, whereas lactate and hydrogen yields decreased. Low biomass yield under thermophilic and extreme-thermophilic conditions benefited higher metabolite production and minimized the accumulation of sludge.