The objective of this study is to investigate the biohydrogen production in a thermophilic temperature at various acid - pretreatment of inoculums and substrate concentration of starch - ri ch synthetic wastewater, i.e. tapioca and potato synthetic one . Batch tests were conducted in 118 mL batch reactor s under thermophilic temperature (55 0 C) by natu ral mixed culture from a biogas plant. Biohydrogen production in ten days fermentation at a range of acid - pretreatment inoculum s from 5 to 6 and substrate synthetic tapioca and pot ato wastewater concentration from 5 to 50 g/L were evaluated. The maximum yield of 19.06 mmol H 2 /gVS added for synthetic potato wastewater and of 18.15 mmol H 2 /g VS added for synthetic tapioca wastewater were obtained at acid - pretreatment of inoculums of 5 and the substrate concentration of 10 g/L. The content of biohydrogen in th e biogas has a range between 41% and 43%, moreover there was no significant methane observed. For the pH inoculums of 5, acetic and n - butyric acids were found as main volatile fatty acid s in the biohydrogen fermentation . The results suggested that the starch - rich synthetic wastewater is one of potential sources of renewable energy from organic wastewater to produce biohydrogen.