Ethanol production ratios of Thertnoanaerobacter ethanolicus (JW200) and two other thermophilic anaerobic bacteria Thermoanaerobacter (65-2) and Thermoanaerobacter the thermohydrosulfuricus (70-1) were determined at different sucroses (15, 20 and 30 g l(-1)) and molasses (30,40 and 60 g l(-1)) concentrations, in batch culture conditions. As a result, bacterial growth and ethanol production ratios were optimum at the same conditions. Also, effect of zinc as ZnSO4 center dot 7H(2)O On the ethanol formation of bacteria were investigated and it was found that, addition of 0.17 g l(-1) of ZnSO4 center dot 7H(2)O to the fermentation medium of T ethanolicus (JW200) was increased the ethanol ratio by ca. 39% and 23% for Thermoanaerobacter strain 65-2. Addition of 0.22 g l(-1) ZnSO4 center dot 7H(2)O increased the ethanol ratio by 80% for T thertnohydrosulfuricus (70-1). The highest ethanol ratio was obtained at the 20 g l(-1) sucrose and 40 g l(-1) molasses concentrations by all the bacteria studied and ethanol production ratio was not proportional to substrate concentration. T. ethanolicus (JW200) produced 5.04 g l(-1) ethanol from sucrose (20 g l(-1)) and Thermoanaerobacter strain (65-2) produced 6.50 g l(-1) ethanol from 40 g l(-1) molasses in modified medium 2. T. ethanolicus (JW200) yielded (Y-X/S) up to 0.47 of ethanol at 15 g l(-1) sucrose concentration. (c) 2005 Elsevier Ltd. All rights reserved.