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Summary Kinetic‐modeling studies are a key step to attain economically practical technology in terms of efficient scheme and bioreactor scale‐up to describe the substrate utilization, biomass growth, and product formation in the biohydrogen production process. Kinetic‐modeling study of biohydrogen production from molasses using mixed culture was investigated in an anaerobic activated sludge‐rotating biological contactor. Single‐substrate with endogenous metabolism and Luedeking–Piret model was used to describe the kinetic parameters at different dilution rate (0.032‐0.167 h−1) with influent concentration of 6, 15, and 24 g COD/L. The maximum experimentally estimated value of μmax, kS, and Yx/s was found to be 0.053 h−1, 9.98 g/L, and 0.11 g/g in dilution 0.167 h−1, respectively. It can be concluded that increase in dilution rate is a suitable for microbial activities in the biological hydrogen production process. Accordingly, maximum specific growth rate and hydrogen production rate will be increased. Contrariwise, decrease in dilution rate is associated with lower biomass concentration and higher endogenous metabolism. Therefore, dilution rate is an important parameter in production of biohydrogen in this bioreactor and should be kept in an appropriate range.