Previously we reported that the hyperthermophilic archaeon, Thermococcus onnurineus NA1 is capable of producing hydrogen (H2) from formate, CO or starch. In this study, we describe the immobilization of T. onnurineus NA1 as an alternative means of H2 production. Amine-coated silica particles were effective in immobilizing T. onnurineus NA1 by electrostatic interaction, showing a maximum cell adsorption capacity of 71.7 mg-dried cells per g of particle. In three cycles of repeated-batch cultivation using sodium formate as the sole energy source, immobilized cells showed reproducible H2 production with a considerable increase in the initial production rate from 2.3 to 4.0 mmol l-1 h-1, mainly due to the increase in the immobilized cell concentration as the batch culture was repeated. Thus, the immobilized-cell system of T. onnurineus NA1 was demonstrated to be feasible for H2 production. This study is the first example of immobilized cells of hyperthermophilic archaea being used for the production of H2.